What usually happens here is the board of a company say to themselves "Let's hire a professional CEO", the next answer then is how, you don't see these jobs advertised on LinkedIn, so they get a talent recruitment agency. For C level management positions there are usually 2 options that control the most of the market, these 2 options have rosters of people from well known business schools with experience ready to step in.
Because the supply is constrained by these companies the CEO pay increases well beyond market rates, as each CEO will earn X% more than the one before it by faking competitiveness, then the former CEOs will complain (as the Mozilla CEO did here) about relative market rates of other CEOs, even though the market rates are set by the cartel that proposed them in the first place.
The board not wanting to rock the boat for the shareholders will generally agree to this extortion for optics, and round and round the merry go round goes.