Topic Dilution is part and parcel of forum slides, but also used on its own to keep a forum population distracted and unproductive. A continual drip of off-topic, red herring, and otherwise inflammatory threads sabotage the forum causing Resource Burn.

If gradual dilution succeeds without raising suspicion, the readers will effectively stop researching and slip into gossip mode.

In this state they can be more easily misdirected away from facts and towards uninformed conjecture and opinion. The less informed they are; the easier it becomes to control the entire group in the direction desired.

Without a proper assessment of the psychological capabilities and levels of education within the group, handlers risk being too far off topic too quickly and triggering forum moderation.
(and they do it for free)