Not really true. The whole existence of a “brain drain” indicates that the places the workers are coming from have insufficient opportunities.

Which results in talent being in short supply.

The talent is both better rewarded and considered and treated elsewhere.

It's quite possible for talent to depart locations based on nonfinancial considerations, or considerations with indirect financial effects, as with noncompetes. The Great Migration and Jewish refugee migration (1920s-50s, and later, Europe) are cases in point.

On multiple grounds, California ~1960 - 2000 offerred both better compensation and better considerations for technical talent. The pendulum is swinging based on a few factors, notably housing costs an conditions.

Or sufficient opportunities, but less compensation.