Repetitive topics and no common sense by some members would be my first guess at why there aren't many active members. Haven't seem a lot of the people online that were here when I first got here (only been back for almost a month)
I am not long a member of this forum but I agree with this. There should be a really big topic, where every member can particpate in. not just a regular topic but something completly new that has the potential to go on forever. so I challenge you to come up with such a topic and you can suggest them here.