Honestly from a lot of women I've talked to , they don't really care about sex that much. Like it's more of a social standing thing to brag to their friends about, or for personal validation, or like that weird flavor of ice cream you enjoy every month but wouldn't eat daily. Plenty of women have a dead bedroom and they'll complain about it but not actually care enough to move on. They love romance novel style sex, where there's all this buildup and intrigue leading up to the main event. Then once all the mystery is gone, they lose interest, they finished that book so to speak. Even if the sex is good, it simply doesn't capture their sustained interest enough in the absence of any other desirable qualities.

Really it's more the romantic idea of sex that they like. They like the idea of a man with a big dick, or a man that can fuck all night, and so on. Maybe they just like that on paper that guy is "better" than other men, he's at a higher rung in the hierarchy so by sleeping with him or dating him they elevate their own status. So yes size still matters even if a woman doesn't want sex all the time, but once you get old enough, they'll start to mature and stop caring about social pecking orders and will start caring about how good of a provider a man is or if he would make a good father and so on.