I've gotta say - I don't really get into mainstream short stories much.
To me, a short story is like a short escape into another world. That's why I usually read genre fiction. SF, fantasies, mysteries, historicals etc.
When done right, the author pulls you into their dream and shows you something new and different. Something exciting and far removed from my everyday life.
Being an adult, I've seen all kinds of drama, known heartbreak and success, lived and loved, won and lost, been both the dog and the hydrant.
But I sure haven't traveled to other worlds, or chased down international conspiracies or traveled through the mind of a serial killer. Now to me, that's entertainment.
So I don't get into mainstream shorts much. But I have read and enjoyed mainstream novels because I think that since they have more room to show and tell you a story, they're naturally richer. They are better able to lure me into the fictive dream and keep my attention. But once again, the premise has to be intriguing and the author capable of not only seducing me - but actually delivering on their promise!