Why are CEOs overpaid you ask. Is it a global conspiracy? Of course not. What makes you ask that? All economic systems and societies have natural incentive mechanism that drive certain outcomes. Why do bakers deliver almost exactly the number of breads people want? Is it a global conspiracy? Are some men working in the shadows scheming and planning this in detail? Nope, that is just how market economics work.
The flaw in your thinking is assuming that whatever a market incentivises must be optimal and ideal. Why is heroin being transported in vast quantities to heroin addicts? Is it an evil global conspiracy? No, again it is just a market mechanism, albeit in the illegal market. Yet, still a market mechanism. There is no central planning. No nefariour conspiracy. But it is an example of how markets frequently do things which hurt society. That is kind of the point. Markets don't represent cool headed intelligence. A market isn't some guy deciding what is optimal for society. Markets are pretty dumb, just like evolution. The incentive mechanism are frequently misaligned in numerous ways.
For CEOs it is a mix of numerous factors. A big part is as simple as culture. If you compare different countries you will find immense differences in CEO salaries which do not correlate with economical realities, but which match very well cultural and ideological beliefs found in different societies. It is no accident that CEO salaries are extremely high in a society such as the American one which tends to worship capitalism and the rich, while CEO salaries are quite low in societies such as the Nordics and Japan where egalitarianism is valued much higher.
It also matches historical trends and fads. CEO salaries began to rise rapidly in the 1970s in the US because various economists claimed that compensating CEOs based on stock market value of companies would lead to better management. Since then that idea has been empirically rejected, but it is kind of too late. Now that way of thinking is part of the culture and upper management has no incentive to really change that now. Why would they? They benefit from it.
Also any complex intellectual task, whether teaching, software development or running a company is hard to evaluate individual performance. You know having a CEO is important, but judging how well CEO A performs relative to B is quite hard to determine. We can judge the extreme cases such as extremely bad, medium and extremely good CEOs. More fine grained evaluation is hard which means the market for CEOs doesn't work very well.
In fact it is not surprising given that most studies show that CEOs actually make very little difference to company performance. Some really exeptional ones such as Steve Jobs and Elon Musk make a big difference, but they are the exception rather than the norm. None of this should surprise anyone. A large part of how a company operates is determine by dozens of managers and a company culture which has evolved over many years. They are probably play a much bigger role in how a company performs. It is a bit naive to think one single guy can have that profound effect on a company of thousands of people.
