I don't think it's necessarily that we have less interest in cultures besides our own, it's more that we usually plan vacations around wanting to see something, like a national monument, or do something, like party at Mardi Gras. Combine that mindset with the fact that the USA is so big, and there isn't much of a reason to ever leave the country because you'll never be able to see everything it has to offer, plus you don't have to pay to fly across the ocean. And yeah, I personally don't know anyone with a passport, it seems pretty rare here. I think one reason might be because of our neighboring countries. Until a couple of years ago, Canada didn't require a passport or visa when crossing our border, and Mexican border towns have been viewed as unsafe for as long as I can remember, so people didn't really go to Mexico except by cruise ships.