It's the Pareto principle. People go where they feel they will have more opportunities, and they take their economic activity with them.
Intra-national economic migrants are able to take their families with them, so they don't have the need to "send money home" the way so many international economic migrants do.
Intra-national economic migrants are able to take their families with them, so they don't have the need to "send money home" the way so many international economic migrants do.