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.
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.