Why are smaller frames so hard to find?

This is my first post, and I wanted to ask the question in the title as it's something that has been bothering me since I started wearing eyeglasses many years ago. As someone with a narrow pupil distance (PD), I have always had a difficult time finding frames that fit my face, and actually, I've never really been able to find a pair of frames that could be described as fitting my face well. (I could probably never wear rimless glasses, due to my active lifestyle.) Based on my experience, it would seem that (on average) the smallest adult frames carried by chain stores and optometrists have a lens width in the range of 46-48mm, which is still too wide for a lot of people. For example, even a 46mm lens sticks out beyond the sides of my face, and actually centering my eyes in a pair of glasses would require a lens probably somewhere in the 40mm range. I read somewhere that a century ago the average lens width was in fact 40mm, and while no doubt human beings have gotten larger over the decades, there is still a sizable percentage of the population that need frames with lenses that small. Why such frames are not made available is a mystery to me, because there is clearly a market for them. If there any opticians out there with an insight into this, I would appreciate hearing from them.