"There are things that have to grow and change from a book into a movie to make it work, cinematically. For instance, in the book, Katniss has an internal monologue going on the entire time and expresses what's going on inside her mind; but in a movie, you can't have that much of the narrator. It was not at all the kind of movie we wanted to make," Hutcherson explained. "So artistically, we had to find a way to convey the emotions, thoughts and ideas through the scene, situation and dialogue without it being expositionist garbage."
Sources: Hggirlonfire.com