Several decades ago, a viable market existed for stories at 5,000 words or more. Now, the market for short stories drops off quickly after 4,000 words. This creates more competition for lengthy stories and leaves writers with reduced chances for publication.
I try to keep my short stories to no more than 3,500 words, usually less. To do this, I place my stories in a single time period and in a particular place with no more than three main characters. Focus is important.
Each word of description and dialogue should support the plot without the reader asking questions. Each event has to relate to the story in a direct way. There should be no more than one subplot, preferably none. Ignoring these points, the word length grows quickly.
Some short stories are just not made to become short stories. They may be an outline for something longer like a novel. If I find that a short story does not want to be short, I try to break it up into several pieces to try to tame it.
It generally does not work. In one case, I gave up and turned the short story into the novel it wanted to be. At the other end, sometimes a novel can be nothing but a series of short stories.
I wrote a book that just did not work. To salvage something out of it, I made five of the chapters into short stories and three were published.
I find it is best to listen to the story and let it grow into what it wants to be.
Quote: Keep writing and the truth is revealed quietly one day.