Earlier quoted context omitted.
> Why would a person who is supposedly having rare skills come to a country and spend their best years here without reasonable guarantee of permanency? I agree with your overall point but the answer here is money. The earning potential in the US vs. e.g. India is drastic.
Yes but if you are worth that money to any company why would you assume one day it will all just end? That's not typical or normal for most careers
Also, you have plenty of people who will have career plans like "work in finance in NYC for 5-10 years, amass a fat pile of cash, and retire to a small farm in the middle of nowhere". If I were living in China or India, I might see "spending 5-10 years in the US earning large piles of money and returning to my homeland to retire and live a life of leisure" as a valid career path.