There’s a key issue of selling complex medical devices over the counter: They’re not configured for a patient’s specific needs.
You can obviously buy corrective glasses OTC, and they will typically make you see more clearly than no glasses at all. But they will never be nearly as effective as getting a custom prescription from an optometrist, including testing the finished product while you use it.
The same applies to hearing aids: Buying one of those cheap devices advertised for a few bucks will also make you hear a bit better. The result, however, will come nowhere near what you can achieve if an experienced audiologist examines your hearing and customizes the device’s processing algorithm with just the right frequency response, voice compression, background noise cancellation, etc.
Further, advanced hearing aids also offer different user-selectable programs for, say, face-to-face conversations, listening to music, etc. Buy a device OTC, and you might never even learn about these possibilities.
Finally, the medical specialist will also always check the overall health of your eyes or ears, respectively, which you will never get with an OTC product.
Considering the sheer complexity of doing hearing aids, and their fitting, well, I have my doubts that Apple will find a way of offering AirPods for that purpose. What’s more, modern hearing aids already offer connectivity for mobile phones, so I wonder what the actual market would be for and Apple-based OTC offering.
FULL DISCLOSURE: I’ve co-owned a store for hearing aids in Germany for a few years, so I’m obviously biased onin favor of specialists ;). But I’ve also seen the power that’s packaged into these tiny devices, as well as the complexity of selecting the right device, configuring it for best fit for a given patient, and training the patient on how to use it effectively.