I could list several reasons why writing short stories are beneficial to writers. Practicing your craft, immediate gratification, and flexibility to name a few. And yes, all of those reasons are marvelous. I highly encourage authors to write short pieces.
But this is why I write short stories.
I want to escape into worlds I've never explored before. Some of them are awe-inspiring. The only science-fiction I've written has been in short form. I love strange planets, exotic aliens, and futuristic technology. I can play among the stars.
Some worlds are beautiful and happy. The perfect societies. What would life be like in a place where we had no environmental or political issues? What kind of problems would my protagonist have when all her family loves her? I love finding the flaws in what seems perfect and diving into hidden cracks.
Other worlds are horrifying. More than what goes bump in the night. What motivates that monster, if it really is a monster at all. Maybe it's fighting against something much more frightening. The tight suspense and hair raising terror. I love to scare myself.
I've written western, sci-fi, horror, steampunk, romance, sword & sorcery, mystery, and fairy tale retellings. I get to jump into these magnificent worlds and hop back out again. There's no limit on the places I can go in my stories, and through short stories, I can go to hundreds of them.
If you're an author, have you written any short stories? If you're a reader, do you read short stories?