I imagine this question is the equivalent of asking someone: Why is blue, red, green, or black their favorite color? It just is!
Beauty is in the eye of the beholder.
Everyone has their "preferences" of attributes they find aesthetically pleasing and sexually arousing. I'm neither a fan of flat chested or big (whatever that means) to some people. I tend to be attracted to those women who are well proportioned for their height and body type.
For example a woman who has a well endowed chest but also has a "pancake behind" would not entice me.
Most of us don't really know (why) we like what we like. We just do.
It's almost a pointless exercise to apply logic towards likes & dislikes.
Some women won't date men who are shorter than themselves.
To each his or her own! :)