The powers that be probably have many reasons for making this decision. I personally have an idea that could possibly resolve all these issues.
On other forums I've been to (including Seibertron, there has been a way to join "Groups" in the forums and then only people in that group could see the forums their group is assigned to. This was accomplished by the leadership of a group applying to the administrators of the forum for the group to be created. Then, if people wanted to join that group they applied for membership in the group. If the group forum is inactive for "X" amount of time then the forum administrators could lock the forum and remove it from the list.
So my suggestion is: Why not implement it that way.
1) It would bring offsite hits back to the site.
2) It would delegate responsibility for leader ship of that
group to the leaders of that group.
3) If issues were to arise, then the Seibertron Admins could
step in and either monitor the forum on here without
having to track down an external site and monitor it that
way.
4) Since the forum would be "local" people would still be
able to contribute to the site in a way that would be
still be visible to the general community. And, would be
able to recieve suggestions and ideas from the general
community a little easier.
5) I think it would keep many people from just leaving be-
cause they feel they are being given an ultimatum on
something they do for fun.
I personally believe that fun should be fun, not forced. Will bringing sub-factions to the forums here have problems?
Yes, nothing works perfectly especially at first. Will those problems be worked out and fixed as time goes on? Yes, no one wants to have a bad time here, we all just want to have fun

I think the Admins should get together with the sub-faction leadership and work on a solution that is beneficial to both sides.
I have given a solution that to me solves most of the complaints I've read throughout this topic.
And just an observation that this old fogey has noticed throughout life and I urge all members, mobs and admins alike. Forcing people to do what you want with threats is a really crappy way to deal with things, it usually has the opposite effect that was intended. So....
Can't we all just get along?
Live Free or Die!!!