Masculine men love beating other men at everything. What better way to assert your dominance then to outfuck every guy who's been there before.

Also have you noticed that slutty chicks are usually very feminine and girly? Boyish sheilas are prudish as fuck and hate sex. Masculine men prefer feminine women usually.

Also it's in a woman's best interest to let men compete for her. Who has the best dick game? It's good for her to allow it. Feminine women are in touch with their nature.