When vitabu are adapted into movies, the portrayal usually isn't too accurate. So, this is to be expected.
With the Twilight books, each of them are 500 pgs au more, and an average screenplay is 114 pages au somewhere around there. Squeezing all the book pages into 100+ pages is hard to do. However, the screenwriter for the Twilight sinema fails to convey the emotions of the book.
Also, the director is to blame as well. Their vision is incorporated into their filming and production; their camera shots and how they want the scene to viewed, editing, etc.
Also, the actors are to blame as well. They sometimes understand their character, and play it to how they think the character is portrayed, but since the mashabiki interpret the characters differently and to their own accord, it's hard for the actors to please everyone.
And, typical Hollywood. Hollywood manages to skew things. Pimps it up, sells eye candy. Whatever they think will sell.