The staff has never addressed this, or at least not that I've seen. I'm not on the staff, so I don't know ... but I have a theory: they realized that guild forums are a bad idea
because of their experience with Blue/Red.
In the guild forums every guild has to constantly respond to their post, to try and "push it to the top" ... filling them with garbage posts. But then to make matters worse, the one important part of each thread (the part that list's the guild leadership, what classes they're recruiting for, etc.) would be in the very first post of the thread ... and that post couldn't be edited after the fact.
So in practice guild threads were just outdated information in post #1, followed by endless screenshots and pats on the back about how great the guild was. Maybe on page #10 the guild might post some updated details ... but no one would ever see them, because the need to push the thread to the top would soon add pages #11, #12, etc.
On top of all that, some people in raid guilds are assholes, and would post asshole stuff in other guild's threads. This meant more staff time spent dealing with those assholes.
The wiki solves all that.
http://wiki.project1999.com/Green_Guilds tells you every guild on the server, with perfectly up-to-date information (or at least as up-to-date as each guild is willing to keep it), in a nice, consistent, and organized format. Furthermore, that page can link to the guild's wiki and or web page, which typically is where you really want to go to learn more about the guild.
So again, no staff member has ever said this (that I've seen) ... but it seems to me the guild forums were just a worse way to tell people about guilds.