Because some French salesman made a mistake a couple of decades ago, from what I've heard. (Feel free to research and prove me wrong, this is what I was told.)
Some manufacturer, I think when commercial looms started coming into use, got the idea that there should be 'signature' colors for male vs. female, and set it up to be pink for men, blue for women, but a traveling sales rep got it backward and pushed it around with pink for girls, blue for boys, and rather than fight it, the manufacturer, and those buying the cloth, just went with it and made it spread.
