I recall an informal survey on the Wikipedia mailing list at some point, and their (admittedly not very scientific) conclusion was that most of the Hindi speakers who edit Wikipedia are also fluent enough English speakers (at least in written English) that they can also edit the English Wikipedia, and for various reasons they often prefer to.
Some of the reasons cited, going by memory, were: 1. English Wikipedia already has more existing content for scaffolding so you're not writing from scratch; 2. English is seen as more official/academic, so an encyclopedia article in Hindi feels wrong, like writing a journal article in Hindi; 3. for India-specific topics in particular, writing in English is seen as a way to disseminate information about India and Indian culture to a worldwide audience; 4. English is more neutral in a within-India political context, without the north-south issues Hindi sometimes has.
Wow. That's pretty amazing, given that Hindi is probably the fourth most widely-spoken language in the world. I would never have imagined it to be used so little online.
Those numbers are mindblowing- is there some kind of India-specific Wikipedia analogue where articles in Hindi tend to go to?