Firing people is also an awkward and deeply uncomfortable experience that all but the most depraved of psycopaths would rather avoid at all costs. At least in corporate settings you can probably coast on shit performance for at least a year or two before getting the boot. Most big HR departments also have performance improvement plans they put people on when they're teed up to get fired, as a CYA against wrongful termination lawsuits (see, your honor, we tried!). So there's a couple of latches there that have to be opened before the trap door swings out