Same reason people buy diamond rings, gendered deodorant, banned nonwhites from boxing, etc. Culture rules. People are not far-sighted logical market agents.

Same reason people buy diamond rings, gendered deodorant, banned nonwhites from boxing, etc. Culture rules. People are not far-sighted logical market agents. Consider the opposite: If sharing your salary is so inoffensive, why do companies go to great lengths to stop you from doing it, necessitating enshrined legal protections (that most people are unaware about)?