If women with small breasts are found so attractive, sexy, and desirable, why then do large breasts receive so much attention? Women's breasts are almost always viewed in a sexual context, and women with large breasts are perceived as being innately more sexual than other women. Women with large breasts are presumed to desire sex more often and have less control over those desires than other women. I believe, women with large breasts are seen as a socially acceptable outlet for men's sexual desires. As a result of this social expectation, men may desire sex with women with large breasts because they are expected to be readily available to fulfill their sexual needs, even if they aren't interested in pursuing a long term relationship with them. Men don't necessarily want to date and marry women they or society views as sexual.
On the other hand, I believe attractive women with small and average sized breasts are viewed as potential wives and mothers, because they are perceived as less sexual, and by default, more maternal. Society simply doesn't accept the idea of a sexual mother. From a social perspective, it is better not to be known for your breasts, as you are more likely to be considered a desirable partner and someone they can bring home to mom. If this logic holds true, there is a benefit to having small breasts, even if women do not believe it. This obviously creates a conflict for the woman with small breasts who wants to be perceived as sexual, and the woman with large breasts doesn't want to be.