If they don't have to move countries, it's not really brain drain at all. It's exactly the opposite in fact.
If they did have to move, then they would, and you'd have brain drain. But because they can remain in their communities (while earning the globally-competitive income that they would otherwise have to move for), they now pay taxes to their local government, buy from local businesses, mentor local youth, and so on. When they've earned enough money from their job, they may quit and start a startup in their own community, or become an angel investor supporting startups in their area, rather than yet another bay-area based fund. These are all good things!
If they did have to move, then they would, and you'd have brain drain. But because they can remain in their communities (while earning the globally-competitive income that they would otherwise have to move for), they now pay taxes to their local government, buy from local businesses, mentor local youth, and so on. When they've earned enough money from their job, they may quit and start a startup in their own community, or become an angel investor supporting startups in their area, rather than yet another bay-area based fund. These are all good things!