But isn’t this, to at least some extent, an indication of a poorly-done movie?
The issue of translating literature to film is one of the perennial points of controversy in the movie industry. It’s often the case that movies “ruin” the book by flattening out the story, leaving out important material, or otherwise reducing the nuance and complexity and richness of the literature.
But this is, to a considerable extent, inevitable. The script for a 2-hour movie runs to somewhere around 20-40 pages of written material, whereas even a short book generally approaches a couple of hundred pages. Movies often get criticized unfairly, i think, because the medium itself has some limitations.
Having said all that, though, it seems to me that a movie based on a work of literature should stand on its own. It should not be necessary to have read the book in order to like the film. Whether the film almost ignores the original material (e.g. the Bourne trilogy), or is very faithful to it (e.g., No Country for Old Men), the movie should stand alone. You shouldn’t need to have read and loved the book in order to like the movie.