The issue is that much of this is an opaque process (for both good and bad reasons). People are forced to make an assumption one way or the other, because they have no access to the data. At that point, the prisoner's dilemma dominates.

I don't doubt companies like yours exist, but are they the norm? I've not met one person in real life who has been on a PIP and it was not a case of the manager trying to find an excuse to get rid of him. Netflix's HR got rid of them because they were being used by managers to get rid of employees.