You're being pedantic. One can travel from New York to San Francisco (well, Emeryville) by train but it's going to take multiple days and, even if you handwave the existence of high-speed rail through two continental divides among other things, it's a very long trip. That's never going to be a mainstream replacement for even a subsonic 5 to 6 hour flight between a multitude of east coast-west coast city pairs.
If there were high-speed trains that could make cross-US trips in, say, 15 hours, and at comparable or cheaper cost vs. airplanes, I can imagine there might be demand. I would be willing to take those overnight.
But even if we could replace most <500 mile flights along the most popular routes (starting by connecting cities up and down the coasts), it would be a huge win as far as fuel economy is concerned.