They don't consciously conspire - they give each other advantages as a natural outgrowth of how they were raised to believe that men are more competent, or that men deserve to rise, or are natural leaders, or because, being raised in a place and time when men worked and women mostly stayed home, they believe that's the natural order of things. No one is accusing them of conspiring against female coworkers - they just naturally raise eachother up because of unconscious bias, and because men already occupy more positions of power.