People move out of desperation. And, it depends on the class. The middle class sometimes moves where there's money: programmers from Asia for example, but I have lived through emigration and I have to say that it is one of the most traumatic moves you can imagine. In some textbook terms, my parents moving from Romania to the U.S. in 63, resulted in better material conditions. But the toll this took on my parents (and therefore on me) is indescribable.
On the whole, people want to stay where they grew up, living in the culture with which they are familiar and sharing their life with the family and friends they have. Of course, the more dispossessed they become, the less they have to lose.
But don't kid yourself. The first generation basically immolates itself on the pyre of immigration. By the third generation, everything is back to "normal." It takes a while though.
As John Donne put it, "Solitude is a torment not threatened in hell itself."
Joanna