it is so that when they make babies in order to be normal, the kids are going to need a nice doodh-dhuli mother who they can love. else they'd never be able to love their wives once they grow up.
So a not so doodh-dhuli mother doesnt deserve love from her kids, even though she has showered her best on them, whether being doodh-dhuli or what. Im sorry but im not getting the point here.