I handled a case involving a woman whose husband burned her on a daily basis with hot oven racks from a toaster oven. For a year and a half.
Why didn't she leave? She had, once, and he tracked her down and snatched one of the children back to stay with him. That child, and the other children, had severe emotional problems. The burning started once she came back because she feared for the life and well-being of the child he took.
He threatened on a daily basis that if she ever told, he would kill her. She believed him. He threatened to kill the kids. She believed him.
She was every bit as much a prisoner as someone in a concentration camp. She became numb and concentrated on surviving each day so her children would not be left alone with this monster.
Leaving is not simple when abuse is involved. Statistically, abused women are at highest risk of being killed when they are in the process of leaving.
It IS possible to help a victim of abuse to plan to leave safely. But it is never as simple as just walking away and "going NC". Women are stalked once they leave. They are in unfamiliar surroundings. Often while they remain with the abuser they can see when an attack is coming and prepare for it--not possible when they are ambushed once they leave.
Certainly everyone in an abusive relationship should be encouraged to take steps to get out of the situation. But it must be done carefully and safely, not hastily or without planning.