In all seriousness, the accords of madness are some of my favorite in-game books. But only 3 out of the supposed series of 16 are actually in the game it seems. I'd love to hear about Sheogorath making fools of the rest of the pantheon, Aesop's fables style, so why do we only get to hear about these 3?

Because Beth didn't decide to write more.

I believe that there were only three created for the game, but have to agree with you that I too would enjoy reading the stories of his consorting with other Daedric Princes.

Write your own.

Well, considering it is "Of Madness" there could only really be 3 ever written and meant to be written.