I mean tbf (at least in my case as an Egyptian) it's not just the high salaries. Maybe Egypt is an extreme case but this country just has no future. The regime isn't just dictatorial; it's also dumb. There's almost no money going to scientific research, the system as a whole was outdated 50 years ago, the military is monopolizing everything and undercutting the market because they can use ~~slave~~ conscript labor and don't pay taxes, etc etc. I'm firmly of the opinion that this is at least partially caused by Britain's unwillingness to fully decolonize in the 1920s and their godawful decolonization in the 1950s, but the fact remains that these countries have a duty to their people that they're not fulfilling, and that's why brain drain happens.

As a living example of said brain drain, salaries were near the bottom of my priority list when I made the decision. I was more concerned about living somewhere where I don't need to worry about being arrested because I said my opinion on the internet (or even just complained about prices) or because I do my prayers at the mosque (I was actually told by my mother to not go to the mosque all the time because I might get arrested. It's that bad). Below that were things like a sane administration that actually cares about things being even just barely functional, a decent education system and academia and the ability to have confidence that the country will actually exist in 20 years. Living in a wildly different country (especially as a Muslim in Japan as is my case (halal food is a pain to get here)) is such a pain you couldn't pay me to do it, but it's hard to turn down actually getting to have a future.

What I wanna say is that it's not just the Global South being undercut by the West; many Global South countries are failing at fulfilling their responsibility towards their constituents, and that's why they're leaving. Now how much the West was involved in creating this situation is another story, but you can't reduce it to just high salaries. Global South governments, as a rule, aren't interesting in solving their own problems. That's why the problem solvers go solve Western rich people's problems.