I'm not the biggest fan of Nicki Minaj, but I definitely agree with what she's saying here. I've always felt that the lack of women CEOs and the lack of women in leadership positions more generally has less to do with blatant/obviously hostile discrimination against women and is instead tied to more subtle, deeply-rooted sexist beliefs within our society. Essentially, qualities such as assertiveness and charisma are still seen as "masculine characteristics," whereas submissiveness and seductiveness are "feminine characteristics."
Notice how even the meaning of the word "bitch" changes depending on whether it's applied to a women or a man. If a women is called a bitch, it's because she's unfriendly, hostile, unpleasant (or possibly assertive/commanding). If a man is called a bitch, it means he's a coward or a wimp (or possibly submissive). I've always felt that a large part of the reason why there are fewer female leaders is simply because many women are not raised to be assertive, charismatic, demanding, aggressive, loud--all characteristics that are valued in a leader, and unsurprisingly, all characteristics that are considered "masculine."
