Yes, there are 32 Discworld novels. I shudder.
It’s not that I particularly hated the Discworld novels - in fact, I have fond memories of reading the first eight or so when I was living in England in the early nineties, very lonely and very scared and very much in need of a fantastic escape. They’re just, unfortunately, not very good books. As the boy put it, Pratchett has about eight jokes and none of them are sustainable over that many stories. Good Omens is by far the best thing he’s ever done, because Gaiman made him break out of his bloody rut!
No, what upsets me is that it’s the mediocre series that go on, and on, and on, and on, while the truly bad ones (usually) get killed and the good ones (usually) end on their own. Why can’t there be thirty-two books worth of Philip Pullman, or Mary Doria Russell, or Tad Williams?
The easy answer is that good stories need beginnings, middles and ends. A story that’s intended to go on, and on, and on can’t be as good as one that’s got the structure built in from the start. Unfortunately, there are other genres that manage the ongoing-series thing quite well. Andrew Vachss, for example, sustains his hard-boiled Burke series for a good fifteen novels and hasn’t yet jumped the shark (though sending Burke to Oregon came close). The Burke novels each have their own internal structure, but the larger series seems designed to go on indefinitely - and yet the books are generally excellent.
I’m not sure I really have an answer, other than to theorize that the reading population occasionally has really, really poor taste. (This would also explain the entire career of Michael Crighton, so Occam’s Razor inclines me toward this theory.) Nevertheless, I wish the good writers would write more of what I like, and that Pratchett would find himself a really, really absorbing day job.