As soon as there's a fiduciary duty to maximise ROI, morals go out the window. If you as an officer resist, the collective of shareholders will replace you with someone who will make more money.
There's a dissolution of responsibility that comes with the distributed nature of shares. The owner of a private company probably feels a certain amount of responsibility for the welfare of their workers. I'd be willing to bet most Amazon shareholders don't.
It's probably a naive opinion to hold, and I'm not saying every Amazon shareholder is personally responsible for the warehouse workers that can't use the bathroom without fear of reprisal, but the system is rotten.