It's the same reason as to why my cousin didn't leave the Caribbean until the crime problem became awful.

If you're a professional in a low to middle income country that's stable, you have a decent level of living that while not quite comparable to first world equivalency, the status of being a professional combined with being able to afford servants reduces the incentives to immigrate. These types tend to leave when the government starts to hunt them down for holding the wrong opinion on things, or if they're gay or feminists.

OTOH, the college educated types that leave are those who didn't win employment in their field, and they're unemployed or stuck working in a low income job with zero hope for marriage.