literally they are looking for imperfections on the natural diamond.
as an engineer this is the difference between a hand sewn shirt and a machine sewn shirt, objectively, why would we pay more for worst quality?
de beers says it's about history and how long that gem stone have existed. but I personally, feel paying 10x for worst quality is a sucker thing to do
Basically any fine detail work, or and stitching meant to create a 3 dimensional shape will be superior when done by a skilled tailor than by a machine.
This of course costs more and doesn't matter for t-shirts or other informal garments.
I know there are sellers that claim to know the provenance of the diamonds (can trace them back to the mine), but that would be the best place to introduce them into the chain. For every truck that goes out half could come from another truck and half from the ground.
It sounds similar to paying for a knockoff Hermes bag