The only reason the global Chinese speak standard Mandarin is because you all agree it's a common medium. In India, there is no such agreement although Hindi is quite close to being there. No non-Hindi speaker wants to accept it as their language. Same way, no Singaporean non-Tamil Indian wants to accept Tamil as the lingua franca. I proudly don't speak a word of Tamil despite being here so many years (well, I do speak a little out of respect as an average Yank speaks Spanish but that's about it).
I am a lot more comfortable with Urdu, Hindi, and Punjabi which means I am more mutually intelligible to Pakistanis than Southern Indians (although some of them may learn Hindi/Punjabi). I deal with a lot of Bangladeshis in my line of work, so I have picked up a smattering of Bengali in recent years. I also speak half-baked Marathi as I used to live in Mumbai. I also speak not bad Gujarati.
That's just the way Indians roll. We call it unity in diversity.
@Joe Shearer