Well for one, the cost of living in India is insanely lower than the United States much less San Fran.
What would happen to you if your company flew you to Mumbai, set you up in an apartment and arranged for you to go to an office, and then went bankrupt before they could get you home?
You'd be responsible for airfare home, and that might or might not be a hardship for you.
Now consider the opposite case, with people from India being paid $1.21 an hour in SF. Can they even afford airfare home? Unlikely.