Why did IMDB get rid of it's forums?

There were announcements from the Amazon and IMDB teams to the effect that the boards/forums were not serving the purpose they were created for. It seemed to them that the discussions were becoming negatively charged on many accounts and tending to be inappropriate and/or downright lewd in many cases. Cleaning that up was increasingly becoming a task for them and it did not seem to be something they were keen on constantly resolving. The proliferation of trolls spelt doom for the forums and they decided to do away with it altogether.
It was a sad end. This portal (moviechat) is a good alternative, and thank god for that, but still, it's not the same. Not much discussion happens here (at least not as much and sometimes, as deep as the IMDB forums were)

I think the main reason was the space the boards took up on their website. That, and the fact that anonymous cowards were ruining the experience for those that legitimately wanted to discuss movies in a positive social environment