My entirely non-scientific hypothesis: Sexism is so rampant in the workplace that people assume a woman must be hyper-driven, bordering on ruthless, in order to ascend the corporate hierarchy. They probably paid a hefty cost to play the boss and it is logical to consider them a professional threat. Some might argue that a certain degree of fear and mistrust comes with respect. It just reads differently because we are unaccustomed to seeing this power dynamic play out with women in superior roles and men in subordinate roles.