I think it's a function of size, imref. Europe is tiny so a good quality train can get you to where you want to go in a decent clip. In the States, a cross country train ride would be unfortunate. We're also generally pretty big on owning cars. That whole American individualism, need for space and love of independence that can't be had when you're stuck in a box on rails stepping over someone's knees to get to the restroom you'll share with five other people.