Why does he do that?

I am in the middle of reading the book Why Does He Do That? by Lundy Bancroft. He does an incredible job of explaining the dynamics of domestic violence and attempting to explain why abusive men are abusive.

Chapter 10 is a great chapter title "Abusive Men as Parents." At one point he discusses the mixed messages that society sends mothers who are victims of domestic violence and he said something that really struck me. He talks about how when mothers choose to stay with their abusive partners, child protection officials threaten to take their children away and claim that they are failing to protect their children. But then when a mother leaves her abusive partner and goes to the court regarding custody and physical placement, the court tells her that she can't keep the children away from their father. Washington County goes even further and says that 50/50 placement is in the best interests of the child. So it is not OK to stay and let her children be exposed to the violence but once you leave, you have no choice but to allow your children be exposed to the violence. How does that make any sense?