Well they are currently split when they should be combined. For instance, CNJ and WHM should only need one forum due to the inactivity in both.
I'm not sure why there isn't anyone speaking of strategies, rotations, and mechanics for specific jobs. We just had a great discussion on stoneskin on the main forums yesterday. There was a great discussion about overhealing, cleric's stance, and threat mechanics about a week ago too.
Perhaps it just takes some effort. The BLM forums are not exactly thriving but a few of us have used some effort to drive discussions about our job. Granted, you'll see it's only 4 of us with occasional input from others. Yet looking at the view count for some of the threads, people are clearly visiting the forum!