For the ones who do not know, JEE is an engineering entrance examination to get into prestigious IITs in India. The entrance test contains questions from the three subjects - Physics, Chemistry and Mathematics.
The question when they are posted on the respective sites, get closed easily as they are homework-like, which I do agree with. But they need a specific platform for free interaction.
And as far as concerns regarding number of users, I think there will be plenty as I have seen many JEE aspirants on all the three sites.