> Why should the organ which tasked to find a mate, to have healthy children with, not work in us anymore?

I can't member where I read this, but I have read that the human sense of smell stopped being hugely important for food when we developed three colour vision.

It's conceivable that vision enhancements also gave us a different path to mate-finding than smell; if so, the smell genes can randomise without much risk to reproductive success.