Yeah, big tech has had it all figured out for a while now. At my company departments would get a target retention number. Going too much under or over that was a problem. If a certain % of employees outside of the top performance buckets weren't unsatisfied with their salaries and leaving, that meant you were paying everyone too much.

It's crazy how much science you can apply to HR once you are working at a scale of tens of thousands of employees. At that point people aren't people anymore, just nameless resources to be plugged into an equation. Kinda like the "a single death is a tragedy, a million deaths is a statistic" analogy. Stack ranking follows the same principle.