>>82561268 (OP)
It's basic evolution.
To the simple animal side of our brain flat chest = hasn't gone through puberty = infertile and not worth mating with (this is also why pedophiles are mentally ill)
But round growths on chest = gone through puberty = fertile and should mate with to make babies.
But the brain is simple and doesn't always know restraint, so it creates the logic "If flat chest no boobs bad and infertile, and bigger rounder chest good and fertile, then even BIGGER chest = even MORE fertile and need to mate more".
Basically, boobs indicate femininity and fertility and make a man want to mate, and a byproduct of that instinct also makes the brain also think more boob = more feminine and fertile.