In some ways it's much simpler that what you wrote, but in other ways it's more complicated.

You need to look at any forum differently. Imagine a group of like-minded people out to get their messages out while suppressing alternative points of view. They have their own secret chat that you don't have access to so that they can coordinate their strategy. That's how they can all work seemingly in lockstep to undermine what you do if even one tiny detail of what you're writing leads people away from any of their preferred narratives.

So a forum is not the communication medium of the shills. It is merely the stage that the general public sees. The communications between the shills are private.