this is a device that would potentially last years though, not months — if you're in the niche of needing something like this you're paying less than $10 a month (maybe as low as $5)... doesn't net out too terribly in exchange for not charging
I don’t understand what you don’t understand. The oura comparison is one they made and used “charging every day” as a reason to not use a rechargeable battery. If they took the oura hardware model and applied it to their voice recorder ring, you would be charging monthly if not longer.
TL;dr - There’s no reason to not have a rechargeable battery other than to create e-waste and “a revenue stream”.