I live 4 hours from the ocean. I know adults who have never seen the ocean, and never will. I know people who have never traveled more than 200 miles from home, never been on a plane, and will die having done neither.
I would love to see statistics on how many Americans have done one trip on a plane t Disney and that's it.
That said, comparing the lack of a second language among US citizens to people living in Europe pointless. In Europe, countries are smaller, and language more diverse. You need to speak other language to function. That said, if you look at lower class people in Europe, and many who live in rural areas, they only speak their native tongue. It's really difficult to become fluent in another language if you don't use it often, and such situations just don't exist in the US. I don't speak another language, but I've managed to pick up tons of vocabulary, so when I'm in Europe, I can order off a menu, ask where the bathroom is, and semi-sort of get directions. Google maps and a portable wifi make European travel much easier than it's been in the past.