The shortage of Americans available for high tech jobs is a combination of intellect, education and motivation. The need for high tech R&D exceeds the number of young U.S. citizens who are properly educated with the strong drive needed to succeed. Culturally, the U.S. has bred two generations of self-absorbed do-just-enough-to-get-by workers.
With a population of 1.4 Billion, the pool of candidates is much greater in India.