You may want to pose this one to /r/askscience. In humans, female breasts are a sex organ, biologically speaking. If you look at other primates and mammals in general, you do not see large breasts, and we know large breasts are not necessary for milk production.

It is actually a really interesting question, and one that anthropologists have discussed in length.

Do you mean sexual or taboo?

There has been research conducted that relates to this. The outcome basically determined that there is no clear reason that men are attracted to female breast. Biologically speaking fuller female bodies are typically considered to be more fertile so there may be an association between larger breast/hips and biological attraction to fertility.