Why do screenplay writers feel the need to completely change things when adapting a book into a movie?
I understand that there are somethings that are difficult to make happen on-screen (though with CGI, this is becoming less of an obstacle than it used to be), and of course time is often limited, but leaving out is one thing - completely changing the storyline is another. It really makes no sense to me why... when a book is perfectly well written, does the sceenplay end up being completely different, or missing giant chunks of the story (parts that usually go a long way to understanding the plot). Glaring examples of this are Anne Rice's "Queen of the Damned", and all the Harry Potter Movies. I know Clive Cussler refuses to let any more of his books be made into movies, because of the butchering job they did on Sahara (which while I actually liked that movie - it was very different in many ways than the book). It just seems like they make a lot more work for themselves, coming up with new stuff - when there is already character descriptions and back story to be found in the books themselves.