It's proof of capability. Sort of like peacock feathers. "Look, I can carry around this obscene tail and still not get eaten! How's them genetics?"

For humans, it's, "I have excess resources I can afford to burn according to the socially-accepted ritual or test, so when you bear my offspring, you can be sure I will also have excess capacity to provide for both you and your offspring."

A female may have second thoughts about choosing you as a mate if you appear to cheat at the test or don't do the test right.

This is the best and most succinct explanation.

That makes it worse.

Not really. If that's what that person values and you want that person, that's what you're gonna have to do. Being a relationship means doing things you don't agree with sometimes.

But why wouldn't she want a larger fancier diamond for the same work?

From a status signaling point of view, it's the difference between a real van Gogh and a reproduction from Dafen Village.

Because it has to be mined.

Its crypto, but with carbon..

and most electricity going into mining crypto comes fron coal