Which they want to sell at inflated 'natural diamond's prices, not cheaper 'lab diamond' prices. So their goal is to try and convince people lab diamonds aren't as good or 'don't count'; pretending natural diamonds are lab grown isn't going to help with that. And would probably make the industry look even worse than it already does once they get caught, which they would

I bought my wife a lab diamond, it's nearly flawless.

You just can't fake that with a natural diamond, it's too rare.