As I understand it, human females are the only mammal whose mammaries are permanently enlarged. One theory is that as we shifted to an upright stance, there needed to be a substitute sexual trigger for ape-style butt cleavage. Humans are also one of the only animals that has recreational sex and female sexual desire.

My theory is that raising a baby human takes a lot of work, so to keep males at home, females evolved a permanent sexual trigger and willingness to get down even when fertilization is not possible.

In other words, breasts are 99% intended to attract and 1% feed an infant. Staring at them is what they're for.

That being said, we've (hopefully) gotten far enough away from monkey-dom that men need to learn to keep their eyes up as much as possible.

A man's gear, on the other hand, is almost purely functional and hence need not be decorative - except no. Unlike other apes, human females need a trigger as well, hence male humans have the largest penises in the primate world. Testicle size is different, I recommend the following:

https://www.theguardian.com/science/2010/may/06/women-penis-size