...I hate to disagree with the premise of the title, but in truth, they are still very much worth it. Many authors have discounted shorter works, or what's known in indie/hybrid world as "short reads," altogether since they make squat when it comes to Kindle Select/Unlimited. But I still write and publish short stories for a variety of reasons, not all of them having to do with making actual cash.
Presently I have maybe a half-dozen short stories for sale under my own label, Bear Pulp. These include Dog Day Moonlight, Pathological, and Bingo Night. All of them not only sell a few copies every month, the majority of them also appeared in various magazines and journals, or were a part of an anthology published by the likes of Down & Out Books. These little devils are a great little marketing tool and also provide a nice creative outlet between novels and novellas.
Still think you can't make money with them?
Let's do the maths (as the Brits like to say).
Setting aside the 50 bucks or so you might receive as payment from a journal for the privilege of publishing your story, say you have 10 stories for sale on KDP. If you price them at $2.99, you make $2.09 per copy sold (I always add a substantial free sample from a novel just to offer up a little more value for the reader and to further market my longer stuff). Say you sell five copies of each throughout the month. That's $10.45 per story, or a total of $104.50 for the month. Doesn't sound like a whole lot, but multiply that times 12, and you get $1,254. That, my author friend, pays the rent for the month (depending upon where you live).
This is a numbers game. Write 20 stories and you can easily double that $1,254. Write 30 stories, and, well, do the maths again. Some authors like Dean Wesley Smith, who is a strong proponent of the no-luck/no-big-ass-promos-required method of indie/hybrid publishing success, has maybe 400 short stories published. An old timer like Harlan Ellison has 1,200 and counting. Both writers are millionaires.
Admittedly, I spend most of my time writing novels and novellas. But short stories most definitely have their place in my canon. By creating short story collections, like my Pathological: Collected Short Reads of Sex, Lies, and Murder, I'm also able to create a book-length product that can also generate lots of reads on Kindle Unlimited. Make the collection available in paper, eBook, and audible and you begin to realize the enormous possibilities short stories still offer up in this new century.