To my view, Off-topic was created to replace Wibbles in a certain level, not entirely.
Wibbles worked as a spam zone to increase the quality of the posts or most likely to avoid shit posts being made here an there, in many forums the spam boards tend to be created for the same reasons, but most of them also get deleted for the fact that they are too bad or tend to get out of control or simply because they draw too much attention leaving no love to other serious boards, in this case it got deleted (I believe) for the three reasons above.
Basically Off-topic was made to compensate the deletion of Wibbles (That is my opinion, I don't even know if I am right) and to make an attempt to give the users what they cried for so badly, and now those users are turning Off-topic into shit. (Read as: Zayex)