A thought occurs to me after reading shoujo stories. Girls never portray themselves or their self insert character with even slightly large breasts unless they see it as a negative trait. Like if they can turn it into looking down on men who oggle them later on, and using it as a chance for character development by showing that the man is bad for this, that's basically the only time they give themselves a chest, and even then it's usually like B cups, that's what women consider huge. In all other instances women really just love to make themselves or their self insert character flat in art. Deep down there really aren't women that prefer breasts.

While men... I don't even have to explain male writers preferences do I? There's a deep psychology to which characters are busty and which ones are flat, based on the gender of the writer.