it's because it's incredibly difficult to get anything passed, the US legislative system has too many checks and balances. Every "check and balance" is another group that has to reach consensus for a proposed action and another point for an adversarial opponent to grind everything to a halt.
I contend that it is better to have a government that can reach consensus easily and act, and that is easy to change if they no longer reflect public consensus, than to have "checks and balances" where absolutely 100% of the government needs to be in consensus to do anything. Gridlock should not be a design feature of a government but that's how the system was engineered (deliberately - it dates from a time when states didn't view themselves as federal subjects but independent states, and this was supposed to help get everyone on board that "no, really, we're just going to do the things that absolutely everyone agrees on", there were many groups who were afraid of being steamrollered without their own special little body and checks on other authorities).
Unicameral parliamentary systems are better - one house to pass legislation, one PM who is a member of the majority in parliament, so everyone is on the same page. Snap elections if they do something that nobody likes, if they don't want to listen to the public then the queen can dissolve parliament and call for new elections.
(the queen actually is a very interesting role in the UK, she is kind of an "oracle" that decides deadlocks between the public and the parliament. When the two are in disagreement about whether to call elections she can resolve the stalemate. She really doesn't do much normally but in times of constitutional crisis can serve as a trusted independent authority - a very interesting safety mechanism that evolved almost by accident.)
It is better to have scrutiny in government - even if it isn't quite as agile.
You can still have scrutiny with agility. That is in fact what I am suggesting.
Firstly, parliament is not unicameral, because of the House of Lords. However, the Lords has a definitively subordinate position relative to the Commons, set down in law and procedure; it's used to do largely non-partisan technical work, like originate boring uncontroversial government bills (like the Air Traffic Management and Unmanned Aircraft Bill [1]), and improve bills from the Commons (it's sometimes called "the revising chamber" [2]). They can't block money bills, and they can only delay other bills [3]. So it's not exactly bicameral, either. Sort of sesquicameral.
Secondly, it's not clear snap elections are actually helpful, because if you need a majority to call one, they will be only be called when the party with the majority thinks it can win an even bigger majority. They certainly aren't a mechanism for correcting a drift between the government public consensus. They were seen as sufficiently antidemocratic that the UK sort of got rid of them, fixing the term of parliaments [4], but it hasn't entirely worked, because the one time a government wanted a snap election, the opposition agreed to it (and then lost by a small landslide!).
Thirdly, the queen doesn't decide deadlocks between the public and parliament. The queen doesn't decide anything - she deterministically follows the advice of her prime minister, because she knows that if she didn't, parliament would finish what Cromwell started. Furthermore the idea of "the public and the parliament [being] in disagreement about whether to call elections" is nonsensical, because that's something that is entirely parliament's decision. Perhaps you think she would take a more active role during a constitutional crisis; i rather doubt that, especially after what happened last time the crown did that [5].
[1] https://services.parliament.uk/Bills/2019-21/airtrafficmanag...
[2] https://publications.parliament.uk/pa/cm201719/cmselect/cmpu...
[3] https://en.wikipedia.org/wiki/Parliament_Acts_1911_and_1949
[4] https://en.wikipedia.org/wiki/Fixed-term_Parliaments_Act_201...
[5] https://en.wikipedia.org/wiki/1975_Australian_constitutional...
(caveat: you said "things" which I took to mean something like "governmental products" which tend to have a high amount of inertia; if you had something else in mind this may not apply)
Republicans are just as adept at constructing things as deconstructing things. Look at No Child Left Behind (fundamental reconstruction of education), the Department of Homeland Security and the TSA (large new bureaucracies), or the TCJA (fundamental reconstruction of the tax system).
I think what we actually witness in government is two different phenomenons. First, Republicans act as a largely cohesive block that requires less coalition building. Second, Republican governing philosophy has as a central tenet the idea that government is inefficient and market-based solutions are better, from Reagan's "The nine most terrifying words in the English language are: I'm from the Government, and I'm here to help." to Grover Norquist's Starve the Beast theory "My goal is to cut government in half in twenty-five years, to get it down to the size where we can drown it in the bathtub."
And the inverse of this is also true, there is an aphorism about the two parties voters, "Democrats fall in love, Republicans fall in line." It seeks to explain why getting voters that agree with Democratic policies to the polls seems to be more difficult than getting voters that agree with Republican policies to the polls. This extends to the politicians, who pick largely from the same menu of issues but at different priority levels. This leads to the Democrats having to expend more effort to build coalitions, an example would be something like healthcare reform. Market-based solutions like the ACA have as much a home in the Democratic party as government-based solutions like Medicare For All (M4A). With a wider gamut of policy positions, more effort inevitably must be spent getting people to consensus.
This means that Republican governments get more of their goals done, and because of their governing philosophy many of those things are deconstructing existing programs. They are capable of putting new programs into place, I named a few but there are others, so it doesn't seem to me that the main difference is constructing new thing vs deconstructing existing things, but the amount of effort it requires to get your coalition to take action.
This all is an analysis of the efficacy of the two parties in accomplishing their goals, without really treading on the more dangerous ground of "who has the better goals?" I, like everyone else, have some opinion no this matter, but to try to keep the inevitable angry responses when discussing politics to a minimum, I'm going to just avoid discussing that altogether.
Does it require less coalition building, or are they just better at it? It never made much sense to me that a pro-choice/drugs/guns/prostitution libertarian from Nevada would vote for the same team as the social conservative corn farmer from Nebraska who wants to implement a Christian theocracy, yet when push comes to shove they seem to ignore each other and vote for the same party. I don't know how to explain that, other than Republicans are effective at pandering to two mutually incompatible philosophies at once.
Broadly speaking, small-c conservatism, hold the following central tenets "...tradition, organic society, hierarchy, authority, and property rights." (https://en.wikipedia.org/wiki/Conservatism, I know this is a wikipedia link, it is sourced to an actual text which doesn't appear to be online and so is not conducive to hyperlinking). It could be that their preference for hierarchy and authority extends to the legislators being willing to support the party leadership, regardless of their own personal policy preferences.
Another line of thought is that there is a Venn Diagram of sorts for those two politicians, and the policies that move forward are the ones where there is already agreement. For instance, we don't see a lot of legislation legalizing drugs or prostitution coming from the Republican party, because while the Libertarians might support that, not everyone does and coalition building is difficult. We do see a fair bit of pro-Christian actions from the party, but I think that could be attributed to reframing the issue as one of Religious Liberty which allows the Libertarian to either support it or not actively oppose it.
Largely though the legislation we see passed through is about areas that likely have broad support where little coalition building is required, tax reform, military spending, moves to reduce the scope of what most Republicans would agree are wasteful government programs.
I doubt the Republicans have found some new method for coalition building, if they had then you would expect more fringe Libertarian ideals like drug and prostitution legalization to have some presence in the conversation. It seems like even in the rather tame Marijuana legalization discussion the Republicans are staking out an opposition stance. Although the desire to make profit from Marijuana has turned some of the most ardent opponents into vocal supporters, as is the case for John Boehner.
This is just the nature of reality. Creation is incredibly difficult and requires immense struggle. Destruction is effortless. It took billions of years of biological evolution to reach a point where a mass of cells can be conceived, nurtured, and grown into a thinking breathing organism capable of manipulating its' environment. One single mindless, simple burst of radiation can completely destroy that. You're battling against entropy. The natural order of things is chaos, disorder, and dissolution. When the will to fight and struggle for an ideal is lost, the inevitable result is decay.
This is just the nature of things. It’s easier to destroy a car than to build one. Same for houses, plants, animals... anything complex, really. Destruction is generally easier than creation.
Especially for things that took a substantial amount of time and effort to build, shouldn't we require much more scrutiny before considering an action that effectively dismantles/dissovles/destroys them? Instead it feels more like we are at the mercy of the whims of whoever is the current temp-employee-in-chief.