The bottom line is that hearing aids today are sophisticated high tech miniature devices, and not a massive market of 100s of millions potential purchasers. Every patient's pattern of hearing loss is unique. As suck, hearing aid designs has evolved along the lines of being customizable for the patient's hearing loss patterns. The hearing aids can be programmed to amplify the frequency bands which the patient is weak in. And they are very good at selectively only amplifying the desired sounds but hardly ideal in the regards.
Those patients have only have small percentages of useable hearing frequency. Even selective amplifying won't help those type of patient all that much. So the latest generation of hearing add are able to digitally compress frequencies ranges the patient can't hear hearing down into the frequency range the patient can hear. Yes computer and electronics can be cheap and mass produced. But for thes type of hearing aided to be useable, they have to small, light, comfortable to wear, sophisticated enough to be customized to the patient's needs and needs to run for long periods of time on very small batteries.
And on a linear note, hearing aids are getting smaller and smaller. The smallest ones can fit directly in the ear canal. Just think of putting a computer with enough processing power to be able to digitize sounds and do frequency compression, and have a sound system to play it back in a package that fits in your ear canal. Think of the engineering and manufacturing challenges.Do you see a mass market of 100s of millions to prices down to $150? ... I didn't think so