I don't think you're correct here. As I've understood the concept for something like a decade, PIPs are almost universally understood to be a soft form of firing. The correct response to receiving a PIP, probably in most SV companies, is to start looking for another job.

It's easy to turn your own logic back around on you. Since it's a more-or-less open secret that most PIPs are part of managed termination, every competent company that issues one knows they're running a huge risk of sabotaging their relationship with an employee by issuing one. There are lots of ways to manage improved performance from an employee without invoking the dreaded PIP. If the company merely wants to improve performance, they can issue MBOs or schedule a special series of 1:1s.

It's also easy to see why companies would issue PIPs despite potentially backing themselves into a corner when the targeted employee exceeds the stated expectations of the PIP. PIPs are how HR wants employees to be fired; they simple are the whole firing process. But that doesn't mean the people who actually write the PIPs know how to write them effectively. In Coraline's story, you have what reads to me like a pretty standard Kafkaesque PIP story: Github wanted her out, HR demanded they follow the standard process, they PIP'd her, the PIP didn't anticipate that Coraline would keep diligent records, and they were forced to go through contortions to pretend that it was the PIP that had been failed, rather than the "will" part of Github's "at-will employment".