It’s not anything like diamonds - diamond prices have slowly and consistently increased over the last 100 years and doesn’t see the crazy 20-30% swings in weekly prices that NFTs and even BTC sees. It’s considered a safe investment with a solid store or value. And dismissing them as “only useful for grinders” dismisses their value in jewelry. If millions find joy in having diamonds in their jewelry then I’d say there’s plenty of use for them.
DeBeers was essentially a cartel, serving in a role kind of like a central bank. They manipulated the supply to keep prices high and reasonably stable and also manufactured the demand out of thin air. Their power has waned some; diamonds aren't worth much second hand anymore, but they're still overpriced at retail and there's still the legacy of marriage conventions requiring a diamond, now with the additional caveat that it must be natural.
The idea of DeBeers is anathema to the ideals of crypto currency, even if the reality of it is far from perfect.
Which company is that?? You're probably referring to DeBeers, but your diamond knowledge is like 30 years behind the curve if this is the case. DeBeers does not have a diamond monopoly! This is a myth recycled over and over on the internet from people making some fake moral anti-diamond stance. DeBeers has less than a 30% market share, and aren't even the #1 producer of diamonds any longer.
The real reason diamonds haven't cratered is because they're a commodity that's always in demand - as long as people want to buy them they won't crater.