There are many such examples. Here’s one from my life: when I was in the pharmaceutical business one of the chemists developed a treatment for a fairly common disease. He and a couple of others tried it on themselves. We could have patented it and run it through clinical trials, but it was something any compounding pharmacist could have whipped up so such a patent would have been worthless. We were a startup so didn’t spend any effort doing a study much less a full program. Instead there are marketed, less effective products on the market.