and why many do not travel, and go in the other side, if the difference is so big? it should not be so difficult for a usa citizen to move between states, and maybe find a new location to live, instead of wasting money in his current residence...
It is easy to say, but for example California alone is likely bigger than your whole country. If I move to a cheaper place, it will be hard to visit family and friends. Plus most companies adjust for cost of living down to the penny, so it isn't like you will really make that much more.