Combination of factors, I guess; HK-cinema going down the drain, and not everyone found the same kind of love for Korean and Japanese cinema, which means there would simply be less to discuss.
IMHO, I also feel the forum got too big when it comes to sub-sectors, so before we basically just had the 'anything goes' for TV, music, world events, games, etc.... So that part of the forum was always very active, but now we have a bunch of dead subfora nobody visits. Kinda as predicted, btw.
Also, people got on stuff like Facebook and whatever, so if there was anything to discuss, news-wise, it partly moved there.
People got older, got into other things, Asian cinema stopped coming to the west as much as it did around the early 90's HK boom, there were too few new faces coming in to replace the old bags that left (or were eaten by cats), and the forum just became more and more quiet, so the regulars would visit less regularly.
Oh, and Brad posted that picture of him giving a bukake to a turtle; that didn't help either.
I was there, the big BNB blackout of november, 2008. We lost many that day...