I understand how branding and marketing could drive the price of frames up, but I've never understood why the lenses themselves are so expensive. The tolerances

I understand how branding and marketing could drive the price of frames up, but I've never understood why the lenses themselves are so expensive. The tolerances are not very high, and there must be a massive economy of scale. The article itself states that they can be made for a buck and a half. Who manufactures those, is there a similar situation as with Luxottica? Why is that market not being disrupted?