Individual authors get their own sub forum based upon how much independent discussion is going on about them and their works. I don't know the actual number but I think it's down to how many active threads are currently running on them and their work. To be honest many of the author sub-forums are pretty quiescent only getting little flurries of activity when there is something new like a new book.On a side note, I was surprised not to see a thread on his work on the Chrons? Have I missed it somewhere? Perhaps he's not as popular as he was about ten years ago, but for a while he must have been one of the best sellers in the UK at least.
ABS
Personally I tend to read the Chrons via the "Recent Posts" button so most of the time I barely notice what sub-forum the threads are running on. If you want to discuss a particular author who doesn't have their own sub forum simply start a thread in the "General Book Discussions" area and others will soon chip in. There have been discussions of PFH here and he tends to get a mixed reception; there are those that love his rich detailed descriptions and plotting and don't mind having doorstops for books (like me ) others feel he pads his books with too much fluff and the books are way too long. Start a thread on him and it will soon filter down to those ideas.
As you say, though, we shouldn't derail this thread into one author!