Some do. Some women live for drama and attention. They get attention from people saying “omgg leave” and get a ton of dramatic stories to tell about how their partner treats them. Others stay for a benefit that the relationship might bring that is perceived “worth it”, for example I stayed in one for a while because we had mutual friends that I didn’t want to lose. Another one could be financially, if you’re unable to support yourself on your own. But it never really is worth it.
financial reasons are a large factor a lot of the time, especially in this economy. Another reason could be mental illness or a bad upbringing. People whose parents never loved them might feel like the abusive behavior is just “how love is” and “normal”, and may be glad just to have someone who claims to care about them. There’s many reasons, but none of them are worth it.