Or because they select for people that are able/willing to make a choice to move across the world/border.
Indeed. Shake a box of rocks for a while and you'll find the largest rocks at the top. It's not because the top makes rocks grow, or because moving to the top makes them bigger, it's simply that larger rocks move up more readily in this environment.
Living in India, Indian schools are mostly worse than American ones—rat race, outdated curriculum, etc. (I don't think there's sex ed in schools even).
> (I don't think there's sex ed in schools even).
Depending on the state, there isn't exactly sex ed in American schools either.