i find it interesting that community projects is more active than gallery... the crowd there tends to be the same, but very dedicated
I think it's probably to do with the content.
In gallery someone shares a creation and others may leave a reply, but nothing else about the creation tends to change so there's not much reason to post again.
But Comm Pro has games, and people will reply, and with each reply or post by the OP there's new content, so there's a reason to keep returning and posting, and that adds up quick.