Well, it's the only forum I know of to spawn it's own "hell" so to speak of banned and misfit posters...that's gotta count for something, lol
There are plenty of reasons...
GAF is pretty diverse location wise. There's almost never a dull moment(downtime), cuz when you're sleeping, someone else around the world is awake and posting away.
GAF also casts a wide news net, and when you're about to hit the "Post new topic" button, you're almost guranteed to be met with "Welcome to..." replies.
The moderation is also pretty good(if uneven).
And the design itself is more geared towards function than flash...so many forums are blitzed out the ass with every feature turned on. Hard to believe that signature banners were once allowed here, lol...that's taking it way back.
And clearly, despite what may seem the opposite at times, the average intelligence level here is pretty high among video game forums
I guess the ongoing lore is what sustains GAF's popularity, tons of "insider" humor, history, notable quotables, milestone events, over the top personalities, etc.
A lot of times, GAF IS the internet for me.