Rail for the US has always been more about moving goods than people. For overland long-haul freight it is significantly cheaper than trucking. Rail allows us to ship goods to places where we don’t have ports or river access. A place like Japan can make such good use of rail simply because it is so densely populated.

The US is also densely populated; when people are talking about high speed rail they are talking about connecting the major, close by metropolitan areas that most people live in.

The Midwest, as an example, has roughly the same size and population as France with a larger economy. In fact, if you overlay the French TGV network onto the Midwest with Chicago where Paris is, you get a pretty good approximation of where major Midwestern cities are located: https://www.reddit.com/r/MapPorn/s/NMr3J3gt8C