A much bigger reason is to demoralize you and convince you that you deserve to be fired, so you won't even think about a lawsuit.
PIPs aren't really good documentation of bad performance; in fact, a badly-written PIP can actually backfire on the company because the wording is usually full of holes a good lawyer can drive a truck through. Basically instead of the company having proof you were a poor performer, you now have proof the company is lying to get you out the door.
A PIP is a lawsuit deterrent, not an actual legal defense.
Not that I like anti-discrimination or wrongful termination laws anyway, though I am willing to compromise. I suggest a compromise to only include certain kinds of jobs like manual labor under employment anti-discrimination laws, where workers are actually commodities that are measureable and interchangeable.
Yet, you've stated you don't want to allow certain people to file these lawsuits, which are usually the only way of trying to correct the problem. So tell me, why is it ok to deprive some people of this remedy simply because of their job title?
PIPs aren't really good documentation of bad performance; in fact, a badly-written PIP can actually backfire on the company because the wording is usually full of holes a good lawyer can drive a truck through. Basically instead of the company having proof you were a poor performer, you now have proof the company is lying to get you out the door.
A PIP is a lawsuit deterrent, not an actual legal defense.