> HR starts to collect documentation describing how the employees performance isn't acceptable, at that they were warned on such and such dates, and that all efforts were made in order to rectify the situation before an actual termination.

I think this is a response to inexperienced, immature, or thin-skinned managers. The company doesn’t want to be on the hook for some manager’s attempt to fire someone and have it be an illegal firing. Since there’s typically no day-to-day log of behavior, HR has to begin documenting things. The only thing they can be certain is “safe” for the company is to fire for underperforming. So let’s begin the paper trail…