Americans don't travel as much, even in the US. They don't have much holiday time.
Many Europeans don't leave the EU, although I'd guess it's more common to visit the US than the other way round.
US culture between states is less diverse than Europe, but it does differ. Geography and climate differs more, although you need to remember some of northern Europe is arctic, which makes up for not having any desert. I think you'll find a bigger difference between Ireland, Austria, Estonia and France than any four US states you care to pick. If non-EU is allowed how about Belarus, Albania, Iceland and Georgia?
I've been to West Virginia, Texas, Ohio and Colorado. I've travelled through Alabama, by train (brief stop in Birmingham). I've been to/through Sioux City, so it seems I just missed Minnesota. I've not yet met an American who's been to more states than I have! But my parents' idea of a family holiday was a road trip.