I'm not sure or convinced that "so many" of today's women stay in these abusive relationships. Women, certainly young women, today have options and in many cases have just as much opportunity as men, as well as making equal/more money than their spouses or significant others. It's the women of yesteryear, the "housewife" types that had no/limited skills, options, etc. faced with the harsh reality of where would I go, what would I do, how do I live on my own, etc. It's the most significant reason in why so many stayed in such abusive relationships.
Today's young(er) modern women IMO would be "get the out of here" and don't let the door hit you in the arse on the way out. Not only has our culture evolved from "it's acceptable to be treated that way," but it's more like, why in the hell are you even with him, and/or you are frigging crazy to stay with him, etc.