I don't know, this might be the actual reason... or it's just that he couldn't really put the book into film. It's very difficult to do so, some may say it's just impossible since the mediums are so different. But your answer has been used before by people defending this or that director, and sometimes it just seems like a cop out, "Oh, he didn't really care about the book".
P.S. Sorry if I sound a bit harsh. Not my intention.
P.S. Sorry if I sound a bit harsh. Not my intention.