Why should he stay behind? What does he owe to the people of the state of India? If already gave them far more than they would get from most of the poor people.

It is not about owing anything to the people of India. It is about owing himself the pleasure and satisfaction of making his homeland - the place where he was born and the place where he grew up - a better place.

He grew up on Earth. He is making it a better place. Why settle with just improving India? Why not the world.

Simple: because India is a developing country? It needs all the help it can get?

People climb up the ladder because they want to get out of where they are. It's not very often that someone climbs out and elects to go back down to help others.

It also doesn't make sense to stay. If you're an autodidact, you almost certainly really enjoy learning. Where better to do that than a University/think tank?

What better way to learn through osmosis than immersing yourself in a foreign (in terms of familiarity not nationality) cultural environment? Then youre learning every second of every day, if youre trying to or not.

It saddened me as well,

..the environment he moved form was the set of tools that provided the ways to find the solution in that if you constrict free money and other overwhelming free resources you get someone hungry to make changes..