Amazon has something like 100k corporate employees, and their URA targets force managers to PIP approximately 6% of the corporate employees every year, so going from 6% to 10% isn’t exactly a massive change.
I have worked at a few firms that have done this, and I have heard from a few people their managers arbitrarily picked them to get knocked into a lower tier.
Conversely, if they hired a big cohort of bozos one year, you know they would never say, "We would like to get rid of 15%, but our plan is only to get rid of 10%." They would have no problem going beyond 10%.
It is if made overnight!