Trains are just the most efficient way of moving people between cities. They benefit everyone, even people with cars.
You have a business trip and need to go from A to B by yourself? Take a train, it frees your brain and the highway for people traveling in groups or with lots of luggage.
Incidentally it also avoids moving 2 tonnes of material for no reason.
A passenger train in the USA weighs about 1000 tons, plus another 150 or so tons of locomotive, before we add the passengers (seating 80 per car and about 11 cars for 880 passengers).
One of the most recent inter-city routes to open, the Borealis service between Chicago and St. Paul, far surpassed expected ridership levels in its first year servicing 212K passengers over a projected 155K [1]. This comes despite the fact the trip would be faster not only by air but also by car. I doubt we'd see this sort of overperformance if "most people don't want trains".
Most places where people want trains have them (high density places).
This doesn't address OP's comments. To remind you, they mentioned "cheap, easy, high speed travel across the country". I would grant Amtrak is easy. It's not the other things though...
I'll take the Acela over flying any day. It's cheaper and less of a hassle. Time-to-commute is a wash when you do the airport security theater dance + delayed flights on the tarmac.
