It is men's nature to look and get attracted to women's breasts. They feel the main attraction of women is her breasts which connects her femininity and sexuality. Men love a nice cup shape and size of women boobs.
Men love women boobs during lovemaking too. Women have observed that the breasts play a major role in foreplay. Men love to caress and play with women breasts and these attraction is visible when they get extremely aroused after getting a glance of it. The pleasurable part of a woman's body for a man is her boobs.
Men find it difficult to concentrate on the face of the woman while communicating when she has impressive bosom. Men believe it is a culture of looking into the women's boobs and then it is their brain which forces them to look at impressive breasts for pleasure.
The men's love for women breasts have made women think more about their bosom or breasts and concentrate on making them look attractive. This is why many women want heavy breasts to look attractive and beautiful with a natural sensual appeal. Just a slim figure is not enough for adding sensual appeal to the body. Having a beautiful and impressive bosom makes them look perfect to men.
Men don't like to look at women with small or no breasts. A man while choosing his mate looks at her bosom because the appeal of good breasts attract them easily.
There is no such answer to why men love breasts as it is both their nature and nurture instincts which make them fall for women boobs. The urge to love breasts make men look at the women boobs!