My assumption generally is that PIP is a result of "HR engineering" - it's basically a legal way to bully someone out of the company with the worst case scenario being you maximize their productivity and burn them out right before they might've been fired anyway.

There's also longstanding evidence that Amazon uses PIP's just to recapture locked RSU shares after bad financial quarters. Basically, have a bad financial quarter, just tell managers they have to stack rank and fire a few more employees than usual.