Ive done a bit of international travel myself, and one thing that Ive noticed about people in smaller countries is a lack of understanding that America is a HUGE place! With nearly every natural feature in the world. From jungles in Hawaii, to the Arctic in Alaska. You can travel full time in just the lower 48 states alone and never see it all... Unlike some small European countries that can be toured in a long weekend, and trips out of the country are as common as a trip to go buy milk.
On top of that, international travel is expensive for Americans. Yes, we can drive to Canada - where they speak the same language and have virtually the same culture. Or we can drive to Mexico. But unless your just going to the border towns for cheap booze, you save more money flying to the "resort" areas than you would driving.... and if you can fly, why go to Mexico? Why not any of the other 1000 places in the world? People who fly to Mexico usually end up being more travelled... for the sheer fact that they CAN travel more. They have a bit more spendable income.
Other than that, we Americans dont have any "cheap" trips to other countries. We are forced to fly over some fairly large distances to get someplace, and when you consider that most Americans havent seen even a 1/4 of what their own country has to offer, its not that hard to beleive that international travel is a low priority.