After pondering this phenomenon for some time, I've come to a few conclusions:
1) Interpretation. When you're reading a great book, your imagination takes over. In your mind's eye, you've recreated the setting and characters in vivid detail. However, what if the direction of the film version of that great book has a completely different take on some (or all) of those elements? All of those things that you've breathed life into on your own suddenly comes crumbling down and you're forced to watch another person's "incorrect" ideas within your beloved book.
2) Engagement. Reading engages the brain. Yes, I'm going to go all scientific on your ass. Science has shown over and over again that watching a movie (or TV show) is a passive behavior. Overall brain activity drops, and it even disengages during the viewing. When reading a book, your brain emits more hi-beta waves, which means your brain is busier at work. So it's easy to see why you can gain much more satisfaction from books. It's a case of active vs passive activity.
3) Format. The average five hundred page novel takes about 20-24 hours of total reading time to complete. It's so much easier to create a richer story with three-dimensional characters going through all kinds of sub-plots. A movie is two hours (or less) long. A director has to try to take 24 hours worth of stuff and condense it by 1/10th. That's a tough job. That's like asking someone who's 300 lbs and 6'8" to wear an 8 month old's onsie. I mean, you can do it, but it's gonna be painful.
There are several movies that have come pretty close, however. And many will argue that there are films out there that have even surpassed their literary origins. Here are a few that come to mind:
Harry Potter. The books are fun, and rich. The films are pretty good too. Although many who have read the books still long for the movies to be a more literal translation of the novels. Look folks, that's pretty impossible. Overall, the movies did a great job and many fans of the books love the movies too.
Lord of the Rings. Yeah, Merry and Pippin are regulated to C3PO and R2D2 status in the films. The Dumb and Dumber version of Middle Earth, if you will. These two characters are not portrayed this way in the books. Despite the differences, the movies are still pretty awesome.
Shawshank Redemption. This is one movie that many could argue surpassed the book version. I love this film, and it's easily in my top 5 of all time. The novella went by the title of "Rita Hayworth and the Shawshank Redemption." I think maybe the film had an advantage, as many of the differences between the novella and the movie were insignificant.
The Princess Bride. If you haven't read the book, you need to do it NOW! Of course like many others, I saw the movie first and then read the novel. The literary version is much more detailed and goes deeper into the back story of the secondary characters. But I love this movie. I can pretty much recite the words, but I refrain from doing so in order to keep from being struck from behind with a shoe.
Twilight. In my opinion, the movie is a little better than the book. But we're comparing shit to shit here. I'm sorry for offending any of you Twerds, Fanpires, and Twihards. The novel was horribly written. As a heterosexual dude, there was no adolescent female fantasy nerve that was struck while I ploughed through this terrible book. The movie is still bad, but not nearly as awful.
Can you think of any other movies that come close to the original books?