Being in that situation you are living in constant fear and also denial that it’s actually happening to you, you justify it in your own head about how you deserve it and that you’re the bad person. It never really feels as black and white as he hit me that’s wrong leave him, it’s often very complex with lots of layers and the victims are usually never believed until it’s too late so they do stay quiet knowing that if they dare tell and aren’t believed their beating will be even worse than usual.
Social services were alerted by a person in a trusted profession who became aware of the abuse (I can’t go into details but read between the lines).