The thing is, if a man doesn't like small breasts, he won't approach a woman with small breasts. A woman could really like a man but not know his penis size until it's revealed. She could then reject him based on his size and that could really hurt him. A woman doesn't have that problem because a man that doesn't like small breasts isn't going to approach a woman and say " hey, I find you unattractive because your breasts are small " unless he was an insensitive ***.

Also, penis size can often coincide with vaginal orgasms. A man can have an orgasm inside a vagina, it doesn't matter how big or small her breasts are. Also, at least a woman knows there is surgery out there to increase breast size. There's not much if anything you can do except get minimal penis size gain by surgery. So men are stuck with a small penis, women at least know there is a solution to small breast. But many men don't even care about breast size like myself anyway. But many women do care about penis size.