The East and (to a lesser extent) West Coast already do have quite solid coverage by train. High speed would be nice but the population density is also such that it probably isn’t worth it because of the frequent stops.
But yeah. People really forget the scale of the US. Our one country is roughly twice the size of the EU. And while we have the densely populated areas that are comparable to “France to Belgium”, we have a LOT of empty flyover states that are comparable to the ass end of Norway and so forth.
And in actual civilized countries? It is REALLY easy to take a train to a population center. Small town? You are probably catching a bus or renting a car.
Don’t get me wrong. The US needs a LOT of work and, from looking at the amtrak route, there are a few extra lines that would actually connect the midwest/southwest pretty well. You still wouldn’t take a train from NYC to California but you might from Kansas to Chicago or whatever.
But most people come at this from “a really rich and privileged white guy told me that Amsterdam is heaven” and don’t seem to realize that our actual cities aren’t THAT much worse (unless you are a cyclist. cycling is suicide in a city) and that Amsterdam doesn’t have to deal with a North Dakota sized dead zone of all civilization and infrastructure.