Warby Parker's frame selection is limited though. They mostly only have large, heavy plastic frames, and the few wire frames they have are still huge. None of their frames suit my preferences or my prescription.

I prefer smaller, traditional wire frames because that's what I've always worn (and at this stage in life that's unlikely to change). Unfortunately, wire frames seem to be out of fashion and no-one seems to have a good selection.

Furthermore, I have a fairly strong prescription and with my current frames, the lenses are about 8 mm thick at the edges, and my frames are the smallest I could find. The larger the frame, the thicker the lenses end up being. I could go with a higher-index lens material, but then chromatic aberrations become way too distracting, and I'd rather have a thicker lens than deal with that again.

P.S. Those "rare" scenarios you refer to are not that rare. My mother gets her glasses from WP, and they end up costing several hundred Canadian dollars, about the same as Costco. My mother's prescription is also not that strong or unusual; like most or a lot of old people, she is both near-sighted and far-sighted, and while bifocals might be an option, most people seem to prefer transition lenses (I think that's what they're called).