The truth of the matter I think is that you do not actually need the best.

Most of the time, anyway.

As far as business is concerned, the thing often runs better with mid people with less leverage. They just do their job, don't have any ideas and you can squeeze them.

Because it's not all the best that are leaving. Just the ones not stuck with a mortgage or similar stuff. This cuts the wings of very capable people and completely strips them off their bargaining power. Which is very useful to management.