[owenversteeg]

Funny enough, Miami is one of the few US cities that does have a pretty large rail system. There are several types of rail and it is fairly fast and effective. You can even take the Silver Meteor to NYC with an average speed of 51 mph. That's a better average speed than many European lines over a similar 1400 mile distance. Compare: Brussels-Athens 41mph avg, Stockholm-Paris 54mph avg, Amsterdam-Lisbon 47mph. The fastest EU route over that distance is probably Berlin-Madrid at 65mph, and the Amtrak is cheaper, has no changes, and is usually more comfortable than any of those.

If you want (relatively) high speed, you can take the Brightline to Orlando, 236 mi in 3.5h aka 67 mph average. That's on par with Brussels-Amsterdam (68mph), Amsterdam-Paris (80mph), but indeed far below the marquee EU/Chinese/Japanese HSR routes of 150+ mph average speed.

More generally: large parts of the eastern US had a developed railroad system (and often still do, for freight.) You can look up old maps and see how widespread they were. The economics mostly just didn't work out because as car ownership rose, the population density wasn't high enough to justify them over cars.