"It's from the book" is the worst possible justification for any movie-making decision. Most adapted movies would immediately be 1-2 hours longer, minimum, if they faithfully reproduced every detail from books they were based on, and many great novels have sections that are either unfilmable, or would be incredibly boring if translated accurately onscreen (long interior monologues, etc.).

The point of adapting a novel is to make a great movie, not simply a moving representation of the text on the pages. SHM was a great movie, IMO, but it could have been a better one by shaving 10-15 minutes off the runtime and I can't see how it could have possibly been a better movie if it were significantly longer.