I just did a quick check, and the only faction forums actively in use are Qarth, Osai and Kayolin. For the amount of space it holds on the forum and the extra moderation load, the negatives outweight the benefits. Besides, on a private forum you can decided who gets to see what, who gets to reply where and many more things. It opens up a much bigger number of possibilities to controlling your faction information online. We might look into replacing the faction forums with some sort of xenforo software in the future, but I don't see a reason to right now.