Money, and a corporate culture where being good at your job is, at least in some way, part of the equation.

For instance, a programmer in Spain makes about a third as he would in the midwest, with the same cost of living. He'd also be able to find a job by having skills that fit what companies need, instead of being about being a good friend of the CTO's nephew.

And that's a developed country in the EU. Imagine the same thing, in one of those places that have immigrants that move to Spain.