It is simply a function of power coupled with what is perceived to be carte blanche. It is every sociopath and psychopath's dream to get a job like that. It is extremely common for such people to be severely maladjusted sexually and generally damaged goods masquerading as stalwarts. Same goes for the priesthood. Given enough time, priesthoods attract vicious depraved scum to their ranks and before you know it anybody who was sincere is pushed out.
The Post Office is a perfect example. The average Pony Express rider could not get a job at the Post Office today. It is packed with ratty, greasy thugs who discourage anybody decent getting employment there. Neanderthals need not apply. Nor anybody interested in doing any meaningful productive work or problem solving.