1. Most grad students are also Indians, and the OPT (->STEM) -> H1B is a common path to employment based visas. And US universities are not unreasonably favoring Indians.
2. A lot of Indians are stuck in H1B status, because of the discriminatory and racist country cap. People stuck in H1B for 10+ years as of now, and potentially multi-decades wait in the future, while other countries get green card right away.
3. India does have many good schools, a focus on engineering, a huge population, and not so many good local opportunities.
And at the end of it all, instead of blaming all Indians (do I represent my country when I attempt to immigrate, or am I an individual trying to not live in that damn country?), maybe USA should actually value high skill labor. Handing off a high skilled labor visa by lottery is a joke, instead it should be called a high-luck visa.