Well, when you apply for a U.S. student visa at an U.S. embassy in India
you are asked whether you intend to return to India after completion of
graduate studies. Anyone who declares an intent not to return to India
is usually not granted a visa. So it is safe to assume that most Indian
graduate students in the USA have already declared their intent to return
to India, and in fact U.S. government officials are reluctant to admit
to the USA any student who intends to stay back after completion of education.
So your question is rather strange. Since these people were granted a visa
only because they intended to __return__ to India eventually, it would
be irresponsible on their part NOT to go back to India, not the other
way round, as your question suggests.
Well, you are assuming a uniform viewpoint from all sides of the
American Society/Government. The State department doesn't want foreign
students to stay back. But, the academic departments often do. It is a
Catch-22.
Uday