The feminist movement did not have as much to do with it as did the move towards industrialization. And father did not get custody of children under the age of 7. Remember, in previous centuries, fathers did not work away from home, in general. There was the family farm, or the family business, and the children were needed to work them, but all that changed with the growth of factories.
Families left the farm, moved to the cities, and dad went to work in the factories. It was no longer necessary for him to have custody of the older children to work the farm. And, he no longer had the time to care for the children, after working long hours in the factory. Yes, the women’s movement took advantage of this, but that did not happen until well into the 1900’s.
As for joint physical custody, the best arrangement is bird nesting. The children are kept in one home, and each parent lives in the home for 3-6 months, then they switch. They pay their own expenses while in the home. The children are the least bothered by their parents divorce. They keep their own friends, bedroom, school, etc.