They want people participating in the forums so they have the new “trust” system. This makes use of forums dependent upon behavior in the forum and seeks to reward any participation by relying on people responding to topics, liking and flagging. This then grants people the ability to contribute to their new wiki – this is all free labor thus removing the need to have paid staff to do such work (either forum moderation or wiki/knowledge base content creation.)
And whenever a system for managing a community is created, someone will try to work it to their advantage and there are plenty of ways available now.