Never really have assessed the reasons behind their reluctance to leave the shores of America. Possibly with the country being such a vast place with tremendous variations in climate and natural environmental aspects they can see all they wish to there. Obviously, you can buy the Big Macs, Pizzas and the KFC buckets in every State, so far as I am aware.
I was in the east when the first Gulf War broke out, never seen anything like it,the Americans on vacation there were not for staying a moment longer. The hotel emptied rapidly, a fair number of Brits went home too. A few of us stayed which was good, the hotel management moved everybody to rooms on the top three floors and we got the best of everything at fair dinkum prices.
There was a Prince from Kuwait in the hotel, he had private body guards all over the place, complete with guns. I
I forget the percentage of Americans who have passports, but it is extremely small. Certainly a good country to visit, very cheap, plenty to do and everybody insists you 'Have a Nice Day'
Great for the kids too, Disney, NASA, Six Flags, Film Studios, White water rafting, Mountain Lodge accommodation, Skiing, Drag racing. Main benefits of course are the really nice people you meet, all interested in jolly old England of course. They are all descendants of Irish too, all of them???