Because the organizations who will hire someone who screams at people are either a) under enormous pressure, b) manned by psychopaths, so your boss's boss eithe

Because the organizations who will hire someone who screams at people are either a) under enormous pressure, b) manned by psychopaths, so your boss's boss either does the same thing or is a cool cucumber who exploits those with less self-control, or c) dysfunctional to the point where they cannot see what's happening or correctly evaluate candidates. It's frustrating and an incredible waste of human potential. That said you are right; you should also raise the issue to upper management. You have more options than just speaking to them directly.