My honest answer is that I think people come here because it's a message board where there is some expectations of intelligence/writing ability. On the few fan message boards I frequent, there is so much stupidity, misoginy, racism, ignorance, anger, and lastly, more stupidity (completing the stupidity sandwich) that it's impossible benefit from spending any time there.
Not everyone here is a poet, but for the most part, you have to be able to express yourself to get your point across. You have to do it cleanly and eloquently.
We have our morons. Sometimes we have a small army of them. But there are a lot of very smart people here who know a lot about sports, life, and art (be it music, cinema/television or writing). I imagine the interlopers who stumble upon us are drawn back for the same reasons most of us are drawn here. Because there are smart people here.
One minor, unrelated, quibble: Occasionally I'll run into industry people who will ask me why I post here. They think it's too gossipy, too stupid, a waste of time, a pathetic exercise by pathetic people.
"How do you know this?" I ask.
"Well, because I check out the site every day," they say.
"So you think the people who post there are losers, but you read their posts every day," I say.
"Well, some of the stuff is interesting," they say. "But I'm not going to bother to post."
"So basically if everyone took your haughty attitude, the site wouldn't exist," I say.
"I guess," they say.