I've thought about this a lot. My personal theory is that when young leave their home communities to seek opportunity elsewhere, that experience changes them. Afterward, to the extent they return, they rejuvenate their community. To the extent they don't, the community stagnates. The reality in the US is mostly the latter. This also created a self-perpetuating cycle, since who wants to go back to their stagnant little corner of the world after getting a taste of cosmopolitan life?
So all that said, I imagine a hugely beneficial policy would be one where young people who leave for college would get assistance paying off student debt if and to the extent they return to their community afterward.