That's because those $20 glasses are objectively worse than $200 Costco glasses. You might not think that the latter is worth the increased price, but for the vast majority of Americans it is.

Btw Zeiss (known to HNers for making EUV lithography hardware) also makes glasses and you can buy them online. Some of their lenses are $700. Not worth it for me, but I can definitely see how someone would be willing to pay even more for those optical specs