If the US was a smaller country tucked in the middle of other smaller countries and Americans were forced to interact with them on a regular basis then yes, Americans would have a much better understanding of other cultures. 
  
Many people in the world fail to understand just how big the US is. You can drive for days and days and never run into a drastically different culture than your own. You might hear a different English accent, see bigger bugs, feel warmer weather, etc. But you're still going to see a Target, McDonalds, big oil gas stations, etc. The laws will be the same, the currency will not change and it's going to still feel like America, for the most part. 
  
The answer is that they for the most part don't have to.