It is always dangerous when a non-native english writer is trying to explain what some third party has said, but I would guess…
- there is groups writers and publishers
- they see each others posts/topics
- there is need to offer ability for writers to block every publisher
Then publishers see what is in ”market” but shy desktop writers can keep publishers in the darkness.
That is a bit difficult to achieve using categories.
Edit: if I am right (because I was in that situation a while ago) blocking is quite difficult because it is forum wide action. There can be other categories where blocking is unnecessary. So it should happend only by writers and target is every publishers, but should apply only to writers-category.