I've wondered this for some time too, and I think the issue is culture. Ask anyone who's moved continents (or even say from somewhere like Manhattan to New Mexi

I've wondered this for some time too, and I think the issue is culture. Ask anyone who's moved continents (or even say from somewhere like Manhattan to New Mexico) and they'll probably tell you there's a culture shock that requires adjustment, even sometimes in the little things. Everything from how the banks operate, what days and times grocery stores are open, and how to get around with what transport all the way to bigger things like ease of socialising with locals or a new language (not to mention nearby family help/responsibility). In areas with easy migration I think there's less of a cultural shift that a person has to go through in order to make it work. That's why it works within cities and states/provinces, and Europe and India could fall into this as well. Even when it is legally and logistically possible, how many people actually do make the move from NY to New Mexico or how many French decide to work somewhere like Germany?