I live in the USA, so let me chip in. First of all, to have high speed rail, you need to have a few big cities that are close enough to each other in order to make a case for the high speed rail transport. But much of the middle America is either rural/agricultural states, or states many mountains or deserts with relatively low population density. So right of the bat, it's very difficult to justify having expensive high speed rail crossing the whole country from east to west. However, in the coastal states, where most of population really lives, and a few places like parts of Midwest around Chicago or Central Texas a good case could be made for the high speed rail.

The second problem with the high speed rail in USA is because of the political lobbying by the special interests, such as the airlines. For example, the triangle of four big metropolitan areas in Texas (Dallas-Ft Worth, Austin, San Antonio, Houston) is a nearly perfect setting for the high speed rail. However, in the 1990s, when the private sector and the government were getting serious about it, the project was shut down by the airlines
(see history here: https://en.wikipedia.org/wiki/High-s...d_States#Texas)

And finally, America has much cheaper gasoline than much of the rest of the world, and lots of good highways. Americans for some reason tolerate longish drives. Americans don't mind driving 300 miles or more to attend some kind of party or visit a friend/family. There is a lot of appeal to driving your car. A lot of American cities basically by design consist of an endless suburban sprawl with mediocre public transport. So if you arrive some place like Dallas on a train, you _still_ need to have a car in Dallas to get around, or call a cab. If you drive your car from Austin to Dallas, the problem is solved. No need to rent anything.