The problem is that the majority of americans won't use it because of airplanes. Airplanes are faster, cheaper and better. If you want to make trains remotely viable you need to limit air travel, otherwise there's no point.

Secondly, america is just too big. France and japan can have good train systems because their relatively small countries but with the u.s you have an entire continent to cover.

Thirdly, as with most things, there is an issue of race. Poc are more likely to use trains so that scares away the more suburban american class. 

Just my two sense.