If someone made a pair of headphones to the same standard as high-end hearing aids are made, the price would surely be similar - and that's just way too much to pay for headphones for most people.

Let me put it this way - if I buy a $50 pair of bluetooth headphones and a $50 pair of normal headphones, put them both in a box and opened the box in 10 years, the first pair will be unusable due to the built-in battery, while the second pair will continue working just fine. Sure, maybe a $200 pair of headphones would have a replaceable battery - but I find it extremely difficult to spend so much money on a pair of headphones.