It goes a little deeper than this. Remenber that bunch of Elsa flash games where the characters are put into grotesque or disgusting situations like getting hurt, dirt or sick and the player needs to "help them" get their shit together? And also the realistic dolls that shit and piss themselves?
These products appeal to developing motherly instincts of little girls, they have a primitive urge to put things back togheter, to clean whats dirt, to aid the sick, to put things in their place, to make order of what is a mess. Before feeling disgusting, they feel the need to "clean" the disgusting