> My understanding about why Amercians don't fly international is the same as the UK used to be - not many even have a passport, and even less have an interest in cultures other than their own.
There's a much simpler reason: the US is unbelievably large compared to European countries. The US equivalent to a London-Rome trip would be Washington, DC-Miami. Another example I give is that I used to live in Urbana-Champaign, which is "near" Chicago, which is roughly commensurate to saying that Paris is "near" Brussels.
And of course, the sheer size of the US also includes a massive diversity of climates and environments. The Florida Keys, North Carolina's Outer Banks, the Great Lakes, badlands in the Dakotas, Yellowstone, the Shenandoah Valley, Maine wilderness, Utah's canyons, Nevada's salt flats, San Diego--all of these places are completely different from one another. Not to mention we have our own Caribbean islands (US Virgin Islands, Puerto Rico), subarctic wilderness (northern Alaska), and Pacific paradises (Hawaii, American Samoa, Guam, Northern Marianas).