I think you're overestimating the effect that visas have VS other factors. Take the country's current socio-political situation as an example Moving to anothe

I think you're overestimating the effect that visas have VS other factors. Take the country's current socio-political situation as an example Moving to another country is no small thing, and most people would avoid it if they had the chance. The fact that they don't means that the cost of changing things in their country is much higher than the cost of moving their entire families to another. Indeed the cost of political change only continues to get higher with the brain-drain. But if were really high to begin with, the brain-drain doesn't make that much of a difference.