If that's the case, why they PIP a certain percentage of people every year? Same applies to Meta, too.

Cultural inertia IMO. If youre growing headcount like gangbusters, the PIP quota is arguably reasonable as a forcing function for bad hires. When youre holding steady or shrinking it's much more toxic in terms of incentivizing politics and killing institutional knowledge. But it's "how we do things".

need to crack the whip even for boring work