ORIGINAL: happywing
I can't speak for the folks who run this site, but I bet it has something to do with man-power. It would take more people (people they don't have) to splinter the site up as suggested.
And also more people to moderate those new forums. Right now it is difficult to keep up with the massive amount of messages, tickets, and help requests, and adding more would make it tough to adapt. Not impossible, but an uphill climb.