DDR4 is as cheap or cheaper than it was at the previous bottom in 2016.
What really got them was when China stepped up investments in a number of projects to jumpstart some domestic fabs focused on RAM production. The RAM cartel came to the table and signed some agreements regarding RAM production quotas with the Chinese real quick after that.
A huge percentage of China's economy depends on smartphones, laptop, desktop, server manufacturing and they had no interest whatsoever in seeing that drastically slowed down so that Samsung, Hynix, and Micron could enjoy a fatter margin.
Not like a majority or anything, but losing 10-20% off 10% of your economy is a big deal.
I thought the RAM cartel backed off the ridiculous prices when the Justice Department started murmuring about antitrust.