Does Nobody Write Original Screenplays Anymore?

Now Hollywood is making Armistead Maupin's The Night Listener into a movie. It is going to star Robin Williams. I like Robin Williams, but come on people! The Night Listener is such a great book but not exactly one that I read and thought, "gee this would make a great movie." Some books, like Michael Crichton's, are written with movie in mind but some books should just be left alone. I wonder if Hollywood screenwriters charge too much because of the union so the moguls look elsewhere for good stories? I don't get it. I'm ready to be enlightened if anyone has any insight on this matter.