Because the book had a lot of sequels? Because it wasn’t really a sequel as such but kinda was in what would now call a sort of reboot way? In this way it’s really much more of adaptation (mostly of Ozma of Oz, with added bits.) And it must work eventually, because for the last decade or so everyone seems to have their underwear of choice either twisted, bunched, knotted or simply moist over Wicked. By everyone of course I just mean a bunch of noisy people. I never got round to it myself.