long-haul commuter rail just doesn’t make sense most places in the U.S.
First, remember that when you compare the U.S. to Europe, they’re about equal in area, but the U.S. has half the population. There are huge areas that are much more sparsely populate, which basically offer no incentive to attract a rail, within which no one really has a desire to commute to a large city.
Where there are large cities, they’re surrounded by sprawl. You wouldn’t need a line, but a web of rail lines to deliver commuters to their destination, which means you’d be trying to spend more money to lay more rail to pull in fewer people. L.A. is even worse, because it borders on a centerless sprawl: a ton of people spread over a wide area with lots of commuters, but those commuters aren’t all necessarily going “downtown”. Rail in these cases is just not worth doing.
In fact, rail is really worth doing when you have one long line of large cities, such that you can just lay down one long route between them. That’s basically the topology of, say, cities Japan. The only places that happens in the U.S. is the interstate commutes into Washington D.C. an New York, places that consume so many workers to support employers who can’t or won’t move that those workers can’t possibly live close. You can think of the entire northeast coast as one big commuter fill for these two labor sinks.
Add to all this that there’s just no expectation that you’ll travel between reasonably large cities for work. No one works in Houston and lives in Dallas, or expects to, or would probably want to if it were an option.
It just doesn’t solve the problem the U.S. has.