One of the most obvious examples of this - for generations, health care professionals in low-development nations have been emigrating, seeking higher incomes in the developed world. That's despite the fact that they're almost always middle class or higher in their own country. You could see this in action over the last 50 years across poor nations in Asia, Eastern Europe and Latin America. Currently the middle class is flooding out of various poor Eastern European nations, seeking a better life in eg Britain.
There were about a dozen articles posted on HN about this concept when the Syrian refugee crisis was peaking.
Increased wealth and better access to information and information technology in African and Asian countries is what's pushed the recent migration towards Europe (via Turkey, Libya or Morocco) on the move.
The doctors, etc are a minority. A visible minority, because their move harms their country of origin more than a loss of a builder from a social perspective but still a minority.