The short answer is, "I don't know." The long answer is, "I have a pretty good hunch, but I really don't know for sure." Our application was rejected this year because there were too many vendors selling Asian food, they wanted more variety. Why we got cut instead of somebody else is a mystery. That gig was replaced by other, more sporadic things, where I have far less responsibility.
Now that I think about it, a good deal of the reason why I used to see a fair number of heels is because that farmer's market was in the evening, and was in close proximity to several bars and restaurants. Perhaps people do still wear heels in those situations, I'm just not around to see it. Where you don't see heels anymore is at church or at the grocery store, the two places I'm most likely to visit.
So here's a thought: Does it even matter whether high heels are actually worn? As long as there is some idle desire to have these shoes, and they are bought, manufacturers will keep making them. There does still seem to be an idle desire among younger women to wear heels, but nobody thinks of wearing them casually at all. They are strictly special occasion shoes. Therefore, there is no need for the cobbler because they don't wear out.
Even in my own collection, the percentage that actually sees wear is fairly small. Nowhere near 1000 to 1, but I bet it's like 10 to 1. I should check sometime. That would be another interesting data point.