hearing aids are medical devices, not headphones with passthrough.
The tolerances of safety and robustness alone are worlds apart.
Think about it this way: if a pair of apple earpods break, you just buy another one.
If my hearing aids break, there is a very high possibility of death and dismemberment leading to termination of my life.
Also, I would never buy apple branded hearing aids except under the circumstances where Apple and the FDA come to agreement, contractually obligated by the US courts system, that if Apple decides to terminate that product line, that all information, patents, design schematics, and code are passed to a 2ndary company (it could be one of the current hearing aid manufacturers) for continued support.
There can absolutely be no instance where apple can decide to "lay off the department" and "turn off the update servers" and leave the product unusable, for the lifetime of the patient.
That's the real difference between hearing aids and headphones.