And there's definitely no excuse because trains are hard to put in where the city is already built out. Not impossible, but still challenging. But some cities in Japan don't have trains and accomplish the same thing with really well-managed buses.

Honestly though, every difference I see between the two countries always boils down to collectivism vs. individualism. It's "public" transportation vs. "personal" vehicles. Americans like individuality and car ownership plays into that.