I'm a manager at Google and have therefore been privy to a bunch of PIPs. I know a bunch of people who have survived them and many of them have later gone on and had successful promos. I've seen exactly one case where everybody involved was resigned to the fact that the PIP would almost certainly fail and that is because the person being fired was a raging asshole. A manager who wrote a PIP designed to be impossible would themselves be given shit performance reviews.
Exactly. A PIP is "I don't want to fire you, but you gotta fix some stuff."
Complex environments like Google need to build and retain knowledge. Firing for zero cause is just...well, we have serious things to do, and that's just dumb. I've never seen it.
A PIP isn't just a closed two-way conversation between a report and a manager. In every case I've seen there are multiple eyes on a PIP and revisions to them.
I suspect white collar employees are a lot more likely to sue an employer in general, and PIPs are pretty common across white collar industries. Filing a lawsuit is a lot easier for people who have money in the bank, a flexible schedule, familiarity with the law, and personal connections to lawyers; all attributes that correlate with white collar professionals.