The sites who do manage enough moderator time to structure their information tends to gain a lot of visitors because of the perceived quality of the information.

The big problem is: who should donate the time? Next thing is that it can in some situations be hard to both moderate a forum, as in ending fights, and in activelly help with questions, so it isn't so easy to upgrade a number of regulars to moderators to get the required capacity to administrate/sort/rearange forum threads.