One of the reasons why I like short stories is that they don't waste time. When we read novels, chapters can be wasted on unwated exposition (yes, I'm talking to you, Billy Budd comma Sailor) that immediately loses the audience's interest. However, short stories are mostly snapshots of a singular point in time. With short stories, the author tells the audience only what they need to know in order to fulfill the point of the story.
Or, sometimes, they don't. In "Hills Like White Elephants" Hemingway only describes the singular point in time, when the couple is waiting for the train. He gives absolutely no exposition, the audience can only figure out the specifics of what is going on through context clues. This can either make for a fun reading for an engaged reader or a confusing nightmare for a lazy reader. Is the lack of background information interesting or tedious?