The fact that terrible CEOs obviously exist is what drives up the prices for the ones that are not obviously terrible. It is an extremely high leverage role (see also: Microsoft).

What separates the good CEOs from the poor CEOs isn't something you can readily teach. Some of the best ones have a preternatural ability for the role in the same sense that Lionel Messi has a preternatural ability at his sport, and are equally rare. The majority of CEOs are journeymen with the skills to do the job but not to be great at it. This doesn't mean that average employees are fit to be CEOs; you don't have to look further than startup CEOs, which are pulled from an above average pool of semi-random people, to discredit that notion. It is a highly specialized skill set that is difficult to acquire and most people aren't mentally cut out for what is required to be good at it. The experiment of promoting rando employees to CEO has been tried on occasion across industry with almost universally poor results.

This is true of most professions that command a high wage. Thinking that anyone could be a CEO is like thinking any dev can be Fabrice Bellard. Even if that turned out to be the case in a specific instance, no one should expect it to generalize.