The FDA regulations allowing for OTC hearing aids didn't go into effect until a little under two years ago, so regardless of the technical feasibility, the mark

The FDA regulations allowing for OTC hearing aids didn't go into effect until a little under two years ago, so regardless of the technical feasibility, the market viability of what you're asking for is a recent thing. (Though since using wired headphones with smartphones has been in decline for well over two years, the market viability is still questionable at best.)