@MichaelCule said something about the Discworld not being as intimidating a prospect as a setting for a game compared to other licensed properties, and thinking about it a couple of reasons for this occurred to me:
- Unlike most settings from literature, it consists of a lot of different main characters in a lot of settings, so we get to see a lot more of the world, and how a lot of different types of characters interacted with it and their societies.
- Humour is usually intimidating to try do deliberately achieve in an RPG, but the Discworld books (with perhaps the exception of the first two) are not solely humourous. They are first and foremost about other things (gun violence, bigotry, death, movies etc.), but approached in a humourous manner.
BTW, the new Discworld RPG, recently Kickstarted, is looking quite good so far.