US is very big. Lots of places to go. Need a car to get around, can't fly everywhere. Trains don't go everywhere, because it doesn't make economic sense. Hm. Stuck with cars.

US has tons of very dense areas with lots of places that can be easily reached by modern public transit, should political priorities ever change. Trains don't go everywhere because of a conscious, deliberate and top-down (centrally planned) choice to invest in car infrastructure. Trains of course used to go everywhere in North America, and were economically viable just fine, until cars were artificially made more economically viable. Stuck with cars due to conscious choices of past generations, unsuccessfully looking for external excuses ever since.