As an Indian who came to the US at a very young age (in the early 90s), I would offer a different perspective.
That it isn’t that the best and brightest chose not to stay. It’s that the society and system constantly put up all the wrong barriers and left them no choice if they wanted to actually realize their potential.
I can only speak of (south) India of the 80s before the economy was opened up, and there was basically no tolerance for anyone who thought differently. People were stopped by all the wrong obstacles. Bureaucracies, bribes, an unnecessarily closed market. And that’s just market forces, before we get to societal forces. If you dared to veer off the usual path, you were often ostracized. Silly caste based judgements and such.
That India lost its best and brightest for decades is a tragedy. And I am truly happy to see the tremendous progress that has come in the last 3 decades.
But I hold nothing against NRIs (Non-resident Indians like my parents) who were willing to pick up their very comfortable lives and start from scratch in a new land, rather than to put up with a system that had failed them for decades. We’ve battled homesickness, culture shocks, the constant tug of war that is immigrant identity, and other such things, to arrive at where we are.
It’s the reason why I can nearly instantly relate with immigrants from any country before I can relate fully to those that have never immigrated in either land.