Well the problem is the musical only covers ONE book. Land of Oz books number around 40 books. The musical is far more known than the series of books. Sure everyone knows about Dorothy, Scarecrow, Nick Chopper, Cowardly Lion, O.Z. Diggs, and the Wicked Witch of the West. Most movie fans don't know the other book characters, like Tik-Tok, General Jinjur, Princess Ozma, the Shaggy Man, Polychrome or the Nome King. These characters are well known to book readers but if you only about Oz through the musical, well that gets a "Huh"?
I know there's fans that want to see something that's a little closer to the book in tone. The closest we got was with "Return to Oz"
Wicked appears to be largely based on the 1939 musical with some bits take from the later books.