Try driving from New York to Boston at a normal hour with regular traffic. We flew to Providence over Labor Dat weekend to avoid the crazy traffic.
Beijing to Shanghai is 800 miles and takes 4.5 hours. That’s a bullet train.
There are two major factors that slow down the Acela north of NYC: geography, and conflicts with Metro-North. There are several sharp curves that keep the Acela trains from running at full speed, and the current Acela rolling stock doesn't accelerate very quickly even after passing through these bottlenecks. In the stretch between NYC and New Haven, trains are limited to a 90 mph top speed by Metro-North, and often have to go slower than that.
The curves are pretty hard to fix without buying up some of the most expensive real estate in the country, and dealing with the political battles that come with that. Fixing the conflicts with Metro-North is theoretically possible with just a bit of extra track to allow trains to pass, but operating that way would probably require more cooperation than either railroad has recently shown itself capable of.
This blog post has a good overview (which includes issues south of NYC): https://pedestrianobservations.com/2012/07/01/plan-b-for-hsr...
This one has a deep dive on how to fix one of the curves, which might give you a sense for how difficult these issues are: https://pedestrianobservations.com/2018/01/12/high-speed-rai...
(Trains on High Speed 1 from London to the Channel have signals displayed inside the cab like a TGV so it's safe to go faster)