I've said this before but, when I started on this site, Green Lantern was hot. Blackest Night was revving up, their was speculation about the movies, the Sinestro Corps War was the most acclaimed event in recent memory, and the entire DC forum was all about GL. And it stayed that way for awhile. And they waited... And then the comics were in a post Blackest Night transitions so there wasn't as much talk, the GL movie was looking like it would be a dud, and the talk about the franchise was at kind of a low. And that was when they decided to put in the forum.
Then it didn't help that people still were making GL threads in the main DC forums, and the mods didn't move the threads until the discussions had time to cool, and this went on for almost the duration of the forum. The movie was released and people were bummed about it. So it was just kind of a poorly timed and executed move. I think if you did it in 2009 or whatever it would have worked a lot better and caught traction. But it's not really a good time now.