They probably just left.
They might have gotten tired of the trend of front page posts about the same game all the time popping up, (COD, Skyrim, Zelda).
Probably got banned for putting angry posts on said threads.
Left due to amount of posts that have no discussion meaning on the forums (happening more than you think.)
Some got banned because the new forum rules make it easy to get banned by reports.
Some got banned after angrily defending their point on certain topics.
Personally, the IP Banning, the health bar, the star rating system, and the captcha are the most likely culprits.
This used to be a place where you could put up your opinion very easily.