I am an American who actually lives in eastern Europe. My sister lived in the UK for 10 years.
We were never considered rich either.
It costs a small fortune to travel these days, it has always been costly and the distance is far.
Takes me over 26 plus hours of just air travel time to go back to NV from HU.
The cost of hotel rooms, food in rip off tourist area etc. keeps most people away from long distance travel.
What I found strange was when I lived for years in Hilo, Hawaii many locals never even saw the other side of the Island in Kona. They spent their whole lives on one side only. Guess if you are happy living somewhere you don't need to travel to see what you can see on the internet for free.
Because America is such a big country that has lots of variety from the hot desert to the cold mountains. Americans don't feel the need to go outside the USA because it has something for everyone.
Most Americans haven't been outside their country
they're geographically isolated - take a look at some other random country such as bulgaria: you have greece right below you, russia 200 miles to the left, western europe (Austria) is another 500 miles to the right.
US however have just mexico which is country experiencing a massive drug-war - canada to the north which in many ways is similar to US and then again nothing on their left and right - just ocean. Japan is too far away and so is Europe.
they are still very big country with diversity in nature and archtecture - that is true as well...
You do realize only about 5% of the world's population lives in the USA, right?
stupid generalization