Because different genders taste cheese differently obviously duh. Don’t want to give them NBs an unfair advantage in the Roquefort round
(Serious answer - I think it’s to try and combat entrenched sexism in the sport? There aren’t many women in chess and by making a space explicitly for them you hopefully create a safe space that can encourage more women to take up the pursuit. As it’s a social perspective thing, AGAB therefore really shouldn’t matter because the point is to go “look women!” Not “women are inherently better/worse and so we should segregate on gender”)