Adaptation

I’m about 1/3 through Wicked, and having seen the musical adaptation, I’m somewhat confused. I know movies and musicals based on novels commonly encounter issues compressing the material into two hours of nonstop entertainment, but this example is such a ridiculous extreme, I wonder if they didn’t purposefully throw out 95% of the book to avoid confusion. I should note that I loved the musical, and I’m guiltily enjoying the novel, but suggesting they describe the same events would likely disrupt the space-time continuum and destroy us all.