People do digress. This is why most clubs, organizations, and governing bodies utilize "Roberts Rules of Order" as a template for controlling the digressions. Committees without a chair accomplish less than one with a chairperson; and, it's debateable whether a committee accomplishes all that much anyway. However, since these forums aren't a committee, it's probably not applicable -- afterall, it's all just "free." There is no need to maintain a structure or courtesy, good manners, etc., it's all free. And, since it's mostly Mods and MVPs who are the major contributors AND digressors. Since they are the ones in charge, why does it matter? It's "their" show.
If this IS the case, then there is no need for moderators or rules. No need for threats to ban people for being discourteous. Make it truly free -- make it a free-for-all. Let everyone behave as they aren't allowed to in face-to-face situations. Let it rip! and let it die.