Because, given the gender balance when it comes to people on positions of power (eg company CEOs), this would drastically reduce the career prospects of women,

Because, given the gender balance when it comes to people on positions of power (eg company CEOs), this would drastically reduce the career prospects of women, minorities, etc, since cultures decided on by white males are often hostile to those groups. And we have, as a society, decided to use the law to prevent such outcomes.