It's true that Americans don't do as much international travel as folks from other nations, especially Europeans, but think of it this way... You're an American and you want to travel. Wanna go somewhere tropical? You can head to Hawaii, Florida or Puerto Rico. Wanna go somewhere chilly? Head to Washington, Montana or, of course, Alaska. Wanna see amazing natural sights? Go to Yosemite or Yellowstone or the Rockies or the Grand Canyon. Heck, you can find great skiing, great surfing, great camping, great hiking, big cities, small towns, forests, deserts, and more all without leaving just California, much less America... Compare this with the small and relatively monoterraneous (if you will) countries of Europe, and you can see why fewer Americans travel internationally -- there's little need to.

As for ignorance of other cultures... Find me any country in the world more multicultural than America, please.