That's true, but inactive nipples don't cost anything, which certainly isn't the case for an inactive uterus. I don't know how it works, but I assume that such developments follow some kind of cost-benefit function.

Not nipple related per se, but males do get breast cancer.

And, in weird circumstances, men can lactate. There's even a story about a viking whose name is escaping me who nursed his son after his wife died.