Continuity mistake: When Corrine takes off her blouse, she shows her children seventeen scars on her back that she got from being whipped by the grandmother. Later in the movie, when Corrine is dancing at a party, she is wearing a strapless dress and there are no scars or any signs that she was struck with a whip.
Other mistake: When Christopher is in the bathroom stupidly "dabbing" Cathy's back as she's taking a bath there is a glass block window behind them. The window makes no sense. It doesn't match the era or architecture of the bathroom or the home, first of all, but probably more importantly - what's behind it? Where is the light coming from? It's just this random, standing glass block window with an equally-random light source. (00:34:53 - 00:56:49)
Answer: Because Connie and her husband were related (he was her uncle) and any children would be a product of incest. And if it was ever found out they had children, it would bring shame and disgrace to the family name.