Why are novella's not novels?
Novella
The novella is generally not as formally experimental as the long story and the novel can be, and it usually lacks the subplots, the multiple points of view, and the generic adaptability that are common in the novel. It is most often concerned with personal and emotional development rather than with the larger social sphere. The novella generally retains something of the unity of impression that is a hallmark of the short story, but it also contains more highly developed characterization and more luxuriant description.[4]