I can understand that position, but in practice I don't think you'd like the quality.
One of the big advantages of hearing aides is that they have multiple microphones that have known alignment with your head position. With all 4 mics separated in space, they do a good job of isolating audio coming from in front of you vs from around you.
Plus people can lose hearing in different bands: they might hear bass fine but people with high-pitched voices may not register. Just turning up the volume won’t address that.
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.)
One of the big advantages of hearing aides is that they have multiple microphones that have known alignment with your head position. With all 4 mics separated in space, they do a good job of isolating audio coming from in front of you vs from around you.