I think people come here for depth.
It's not the quantity of messages which matter but the quality. The internet, and life in general, is full of superficial and outright wrong information. This is one of the few places I've found where people who don't know an answer generally leave it to those who do. I feel reasonably assured that if I read a thread about a question about Japanese, the answer will be accurate and not a guess by someone who really doesn't know what he's talking about.
I'll trade away 100 mediocre posts to get 1 excellent post any day.
Granted, that doesn't drive a ton of traffic.