India was completely conquered and ruled by the British for a century or two. China was defeated militarily many times, but was never really conquered, and wasn't colonized aside from a few places like Hong Kong and bits of Shanghai. That's a huge difference in circumstance which I'm sure results in a huge difference in attitudes.

China also had an authoritarian government willing to impose Beijing Mandarin as the standard language for the whole country. I don't know that India's government would have been willing or able to do something similar.