I think it's just too hard to coordinate everyone's schedules so that people would talk. Hell, even when quite a few people would show up on the Yahoo! chat service we once had, no one save a couple or three would say anything. It was really hard to keep up a conversation, and for the most part, people usually exchanged dick sizes and other stats.
"Hey, I remember you. You're Dee from the board, right? How big is your dick again?" You get the idea.
Maybe I'm a weirdo, but I like one-on-one chats through IM. I seem to stay more engaged with those than trying to juggle a few conversations in a chat room at the same time.