What an odd comment. You don't need to move out of the US in order to reduce how much you drive, or live somewhere your kids can walk to school (source: me). Expecting people to make such a drastic change for fairly minor lifestyle changes isn't realistic.

Also, I don't think it's fear that prevents Americans from moving across the world. I think it's more related to, they don't want to leave their family, friends, and life they've been building for the last 20-60 years.