I thought this was old news. US universities have hard quotas per high school, so you’ll have better chances of admission if you attend a poor performing school.
The charts that show changes over time reveal that it is not old news. The change has been happening for a couple years, but before the last year or so it would have been impossible to show that it was a trend, not just a blip. And of course the UCSD faculty report on remedial math shined a spotlight on the issue.