Because the only people technically qualified to prescribe hearing aids are audiologists. How many audiologists do you know? The industry requires you to have a PhD in audiology. Secondly, most insurances do not cover hearing aids/hearing tests even when people need them.

There's a ton of gatekeeping when it comes to hearing aids. Some of the gatekeeping makes sense since hearing involves lots of delicate and small pieces in your ear. I wouldn't want someone without the education prescribing hearing aids for me. However, all this gatekeeping keeps people from getting the help they need.