(Disclaimer: this is by no means the official word, just what I seem to remember hearing at some point)
As far as I'm aware 12oz has run at a loss for most of its lifespan, being propped up at first by Raven personally, and then later subsidized by related projects (4THW, AKA etc.). My guess is that since the relaunch and resultant increase in advertising, the forums now break even, or, if they do make any money the vast majority of it will be ploughed straight back into improving content. From my understanding of what Raven does outside of 12oz he neither needs to nor wants to run the site as a money spinning venture simply to line his pockets. (Anyone feel free to correct me if I'm mistaken)
The bottom line is that server space + bandwidth for a site of this size is not cheap and since most of you are too damn cheap to fork out $18/year (what does that translate to in the US? 6 beers at a bar? That's giving up half a beer a month...), what advertising revenue is generated can only maintain the current server capacity instead of increasing it in line with the growth of the site and/or adding more features. If one day the site can no longer be sustained I'm willing to bet that people who will complain the most and most vocally will be those who are currently complaining that they shouldn't have to support the site financially...