Likely because most public companies are mostly owned by funds of one sort or another which either don't hold the stock long term or own the stock because of indexing. In the former case, the incentive is to select for CEOs who raise the stock price in the short term. In the latter case, there is no incentive for fund managers to influence management at all.

The discussion is why the board does not select cheaper CEOs. In the case of these supposed funds that are not interested in the stock long term, is the claim that a more expensive CEO will deliver them better short term results? If not, why would a fund that cares about short term results want to overpay for a CEO?

Because the people who own companies are either a) disinterested index funds, or b) members of the same plutocrat class as the board members and CEOs.

Why are the people in b) okay with overpaying for something?

Because they're also getting overpayed in a similar situation at a different company. It's in their direct interest to raise the "market rate"

So a significant portion of owners employ each other at each others’ companies?

You're talking about employment as if they're working 9 - 5 in construction. These people are amplified by their networks, they don't work for eachother. The better their networks performs, by connections, or by value, or by whatever metric you want to monitor, the more they perform...

What about private equity firms?