It's only been in the last couple decades that those things have come into the public consciousness. It can take decades to change perception, especially with something like diamonds that aren't usually purchased by or for kids.

Those kids growing up in the 90s who heard about all the shit DeBeers did and continues to do are now of the age where they would be a customer and they aren't buying. The up and coming generations certainly don't value diamonds either.

I would bet that in 15-20 years the market will decline significantly further and the artificial diamonds are only going to hasten that decline.