What determines which spots get chat rooms?

For the House MD Spot, I first polled people with a couple of picks asking if they wanted a chat room. Then I set up a forum that people could "sign" to show their interest. Then I sent a message to the Fanpop Four, providing them with links to the picks and the forum that showed that House fans would love a chat room of their own in their spot. From that, the Fanpop Four decided that the House MD spot would benefit from a chat room and they gave us one!

So my advice is to do that. But I'm not sure how other spots got their chat rooms.