Well they don't even know what's out there. 40% of Americans never left the US, 11% never even the state they were born in [1]. And even if you travel to another state, culturally it will be pretty similar to where you came from - same language, same TV/radio stations, same car dependence, same politics.
In contrast, in Europe... pretty much anywhere outside of Russia only needs about two to three hours worth of car drive and you're in a country where you don't know anything, in the Balkans you won't even be able to read because Serbs write in Cyrillic, and on the eastern border you can even play warzone tourist if you don't mind the risk of getting arrested or shot (or you can sign up for a combat tour with the Foreign Legion). Every one of our countries does stuff differently and you have so many opportunities of learning, it is mind blowing sometimes.
[1] https://www.forbes.com/sites/lealane/2019/05/02/percentage-o...