Perhaps, Hindi should be India's primary language because if we talk about the population, 43% of Indians know how to read, write, and understand Hindi, according to the Indian government's census data on a Wikipedia page. While diversity sounds good to hear, imagine what difference it would make if everyone started speaking the same language. I have seen discrimination based on different languages. Just think, if we set the foundation right...
Now you might think I'm quite nationalist, but what can I do, these questions are coming from my heart. Perhaps this is how significant it is: India's identity is possibly tied to Hindi and the Devanagari script. Yet, even wolrd, still associate India with its population, poverty, and they know that Indians speak Hindi.
It seems you're suggesting that English should be the primary language, considering only 1 or 2% of the population in India speak it. Calling it a bridge for diversity might be valid, but I don't necessarily agree with that perspective.