> And I find it so tragic. It means that the best elements of a given country are being sucked out of it. How can this country ever get better if the best elements just leave it ?

They don't leave irreversibly, they can go back if the political and institutional milieu in their home country improves, and bring valuable insights from abroad. This dynamic has been quite common wrt. those who migrated to the Americas throughout the 19th and 20th centuries.