Big Tits

It is the same reason women are attracted to big dicks. It is sort of an instinct burned into the human brains before we had enough intelligence to know better. It has to do with procreation. A longer penis will allow better implantation of sperm in a vagina, bigger breasts will allow better feeding of any offspring giving them a better chance at survival. Some species of animals will choose their mate because of the color of the feathers, or because their mate can do the special dance the right way or in a way that the other animal likes.