My intuition is that the elected officials are wary of choosing positions blatantly opposite of the interests the lobbyists are pushing for since the lobbyists could easily support a different candidate and put a lot of money into supporting them. So if you don't behave in the way the powerful lobbyists want, they'll get you kicked out of office.

It is exactly this.

You look at donations to people from corporations or through lobbyists and they don't look that large, $15-20k and they are getting big bills passed.

That $15-20k isn't buying the politician or their vote. The threat to give millions of dollars to the opposing politician that will support them is.

There are limits on how much you can donate to a candidate's campaign; however, you can contribute unlimited funds to a PAC, but the PAC's advertisement efforts must be separate from the candidates; they can't be coordinated.

Which is perfect for a company like TurboTax who wants to lobby for an issue... they don't care about the candidate, they don't have to coordinate with them at all... they just tell the representative, "if you don't vote my way, we will fund a PAC that will attack you". No candidate coordination, no problem.

Conversely, people opposed to TurboTax could get their own lobbyist and do the same thing.

As I said in another comment, no one cares about free taxes as much as TurboTax cares about not having free taxes. It is a minor annoyance to every citizen, but it is life or death for TurboTax.

The people who are hurt by not having free taxes certainly can't afford lobbyists, and even if they could... they would have to spend so much more than they pay in tax preparation fees for their whole life to compete with TurboTax money. Who would do that?

Collectively, people spend billions annually on TurboTax. They could, instead, all chip in $25 for their own lobbyist, if they cared enough to not spend $100 on TurboTax.

If they can afford TurboTax, they can afford the lobbyist.

Couple of problems with that... one, not everyone would chip in. Why would they? If there is a fund paying lobbyists, my $25 is not going to make a huge difference.... they aren't going to win or lose based on my contribution, so why contribute? Your money wont change the outcome, and you will get the benefit even if you don't participate... standard Free Rider problem.

You might say that you should donate out to the fund out of moral principle of a just cause, but there are a million just causes, a million small rent seeking industries that do this sort of thing. Which of them do I donate to fight against? Why income tax and not one of the others?

TurboTax is going to be willing to spend a LOT of money to fight this... you are going to have to get a LOT of people to choose your moral cause, and donate to the PAC.... and then find even more when TurboTax spends even more on lobbying to counteract your PAC. Who is going to give up first?

A lot of people are saying that the fear comes from lobbyists and the interest groups they represent giving money to opponents. That is partially true, but money is just part of the overall influence that the interest groups lobbyists represent wield.

In the case of ReadyReturn, one of the key players is Grover Norquist, an anti-tax activist. (see https://priceonomics.com/the-stanford-professor-who-fought-t... for some of the older history here) He has this incredible network of anti-tax groups, media figures, and others that can be activated to attack and take down politicians, particularly republicans, without spending a dime (altough they also have money to spend).

It might seem wrong, but it is fundamentally the same mechanism by which liberal action networks (like human rights campaign or NARAL) drive their political influence as well.

It is these networks of influence that politicians really fear, because they are so much more effective then money.

Lobbyists often threaten to fund whoever will campaign against the elected official at the next election. They say "we will allocate $1M to a PAC benefiting your opponent if you advocate for free tax filing".

It never ceases to astound me how this is allowed and accepted in the U.S. America is the first to complain about corruption in other countries around the world... yet here we are.

We privatized corruption and turned it into a business model

Corruption is legalized here. Changing these laws is hard!

so let me elaborate a bit, all the people that work on this agencies are employees, they are not politicians.

If a politician influenced by a lobbyist start to question the decision of an agency, have hearings, grill the management on the reasons they decided to waste tax payers money, etc. that is not fun for those employees.

There is no incentive for that trouble and people try to avoid it as much as possible.