Other developed countries tend to have parliamentary systems where policy making requires multi-party coalitions. When you need to get three or more parties on board there is less opportunity to get park-barrel spending passed without _someone_ crying foul.
You're describing the rest of the US, not New York. New York is the other way around, where extreme corruption and disenfranchisement means elected officials have no reason to pay attention to their constituents. Sheldon Silver was one of the strongest advocates for cutting bus service, even though his district has no subway service, so they all depend on it.
Outside of city subways: Amtrak's Acela service (which is what passes for "high-speed" though I understand this is weak in comparison to Europe and Japan) was built and established in the early 2000s, and boosted Amtrak's share of the air/train travel on the NYC-DC corridor from 37% to 75%. Boston's Big Dig project, which for all its faults was certainly impressive, spanned a couple decades and was finished around 2004 or so.
Two main things you'd do if you had money and political will to speed this up:
1. Tear out old bridges (some have been "urgently in need of replacement" for a decade already) and replace with modern ones. Locals like how the old bridge looks? Great, hand over the money for a new one that looks the same. No money? You get a generic reinforced concrete bridge rated for 120mph and suck it up. This can be done in 24 hours per bridge for a short bridge, shut the railway, smash the old bridge, drop the new one in, test it, re-open the railway. If you have the manpower you can do ten bridges at once.
2. Eliminate at-grade crossings. These are unsafe even for lower speeds, they're lethal for High Speed Rail and must be closed. If practical add a bridge or tunnel. If not, too bad, close them anyway and people have to go round.
Several large cities in Europe have built new high speed tracks in tunnels under the city.
The track between London St Pancras and Stratford stations in London (and from Stratford further east) is an example. St Pancras is the end of the line, so the speed is necessarily limited by the acceleration and braking capability of the train, but [1] says the speed is 230km/h = 142mph. [2] says speeds in tunnels are limited to 270km/h (168mph), they probably mean a bit further out of the city.
Other than the last 1km or so, the whole track of this route is new.
Realistically, any city worth spending so much money on will have every train stopping at it, so there's no need for higher speeds in under-city tunnels.
[1] https://www.railforums.co.uk/threads/hs1-maximum-permitted-s...
I don't understand why not? Japan's high speed rail was added into multiple major cities without tearing up the whole city. What did they do that can't be done in the US?