The chairman was selected by the other Commission members and could only be replaced by death or if he stepped down from his boss´ position. So it wasn´t only power that put him there but also reverence and seniority (longevity as boss). Mangano was not the most powerful boss in 1931, neither was Bonanno in 1951 but they were both held in highest regard at the time of their election. Castellano became boss in 1976, Gigante in 1981. So naturally, if Castellano was the chairman immediately after he became boss, he could not be removed from the chairman´s position, even if Gigante may have been considered more powerful later on.

I say if because I´m not sure Castellano was the chairman of the Commission right after Gambino´s death. Does anyone know/have any sources for this?