Maybe a rather irrational and uninformed market together with the retail sellers keeping the prices up? As a regular person you have to trust the seller, so you

Maybe a rather irrational and uninformed market together with the retail sellers keeping the prices up? As a regular person you have to trust the seller, so you're not going to buy a cheap diamond on Ebay or something like that. So there might be enough power to set the price with the established jewelers . It also seems to be a market that is mostly based on marketing, so it is maybe more similar to something like designer items where the name on it provides the perceived value, and not the material.