It’s a well known rule that the book is always better than the movie. I mean, there’s definitely some exceptions, but it’s actually a pretty reliable rule. Why? What is it that makes the book so much better? I’ve got a few ideas that I want to throw out there.
A large portion of a book is character thoughts, emotions, and internal stuff. These things don’t translate very well to screen without doing a narration. And for most movie makers narration doesn’t fit well with their vision. (It killed in Clueless, though!) So in movies we don’t get to know the characters as well, and many of the deeper points are lost in translation. The 2005 Pride and Prejudice comes to mind, with entire minutes of Keira Knightly just staring thoughtfully into the camera, all of Elizabeth’s wit and sarcasm inaudible to the viewer.