Aside from the bad/criminal examples, they always seem to fall back on 'competitive wages' - is that real or self-fulfilling prophecy, I really don't know but I want to believe the latter. It's hard to fathom how they could collectively be worth 9 figure or more incomes, especially hearing of examples of other multinational CEOs from other countries who don't pay themselves nearly as much, Japan comes to mind. However, corporate compensation abuses are not limited to the USA either from what I've read over the years.
The compensation committee of a board recommends that the CEO be paid "above average" or "in the top quartile". If all the boards do that, it means every CEO is paid above average. We know that is not possible, the result is a spiral upwards that never ends. Because the companies do not all use the same measures to compare and judge their results, they all can be "above average" in some way. Because the person getting paid is the one that hires the board members and compensation consultants, he/she can stack the deck and reward the effort, and they clearly do.
The real telling signs were things like backdating options and such. No clearer sign of ethical breach and real intent.