With a lot of films, you've only got 90 minutes to work with. Add to that credentials at the end (5 minutes minimum), the credits at the beginning (3 minutes) and the introduction to characters and so on, and you've got quite a lot to pack in. There's too little time for character development, and people get bored quickly if nothing happens in the process.
In a book however, you can pause that for long periods of time, and there's plenty of metaphors and other descriptive techniques to help you understand the character better.
Take a film like Machete - you learn the character's motives in the beginning, what he's like and why he's known as Machete. Danny Trejo portrays a rugged ex-cop who is hired to become an assassin, and later rebels against the people who hired him. In 2 hours, you've got so much and more.
In a video game like Mass Effect, players develop a relationship with Commander Sheppard through three games, and control his every move, decision and mission.
In a book though, you're given a character and have to stick with it. If you don't like the character enough and you've got around 300 pages of him/her/it, you might as well turn back.