The same reason that only 10% are some 'Chinese hacker from Shenzhen'. Indians & Chinese are invested in their local ecosystem, so you are unlikely to see their efforts reflected in the type of western-repositories that we're looking at.

Secondly, India is still a poor country. So open source is produced as a by-product of the commercial work you do, but it does not have the maturity of a made-for-open-source product that ends up having dubious commercial viability.

The main point of open source in under-developed economies is to put out a positive signal for hiring. So the second you've done just enough, you are looking to escape the hell that is 'unpaid open source work' and move to corporate code that might also be open-sourced. Also, the best candidates (IITians, flagship university kids, Bangalore undergrads) are hired through on-campus hiring procedures. So efforts go into improving their signaling towards those avenues, rather than publicizing your work to the entire world.