Second, this isn't corporate head-hunting. We're not going out to other countries, finding their "best and brightest" and forcing them to come to the US. Are you really suggesting that we should refuse entry to immigrants and refugees looking for a better life or more opportunities? That's incredibly condescending. Yes, I'm sure Russia would have been culturally enriched if Irving Berlin had stayed and been killed by the pogrom. Andrew Carnegie definitely would've become Scotland's king of industry if he'd stayed and starved to death there. Albert Einstein surely would've been able to continue his ground-breaking studies as a Jew in 1930s Germany. Sure, some of these great talents might have been successful if they'd stayed, but just as surely others died in obscurity because they did.
it's because those who go abroad for higher education often to do not return to their native land because their governments (which often run just about everything) believe that they can pay returning natives peanuts, simply because they are natives.