Yeah, cartels gonna cartel. When I bought an engagement ring you'd find a natural stone for $x and the lab-grown version was, at best, $0.9x - I came across several instances where you'd choose between lab-grown and natural and the price was the same regardless.

They've been cheaper for a while but it doesn't matter that it's cheaper to make lab-grown diamonds than it is to mine natural diamonds if the consumer is going to pay the same regardless.