Because Queen Victoria had 9 children and they placed the girls in all the royal houses.
According to History Today,
"The newlyweds went off to Windsor Castle for a three-day honeymoon. Victoria described her wedding day as ‘the happiest day of my life!’ and the wedding night that followed as ‘most gratifying’.
"There is no doubt about the sexual intensity involved. Victoria was pregnant within a couple of months of the wedding and, although she would always detest pregnancy and childbirth, she and Albert would have nine children."
#HerToo