Thinner skin, so you can in theory get better sensor readings. And you don't have to convince people to give up the watch they already own. Selling somebody who owns a $4000 watch another watch is an uphill battle that requires Apple watch levels of sophistication, selling them a ring is a lot easier

I also find the cost of the Oura outrageous. But getting the $450 smart ring instead of the $20 smart ring from aliexpress is the buyer's choice. It doubles as jewelry, and some people are willing to spend on that. And the software quality is certainly better than with the bargain bin option