The book is called "More work for mother" because a lot of
labor saving devices saved
male labor by making the work physically less demanding and allowing it to thus be shifted to the wife.
Three hundred or so years ago, most couples were literally working to put food on the table and keep people clothed. They did so by raising their own food and sewing their own clothes, etc. Standards of living were generally lower.
Over the course of that 300 or so years (because I probably read the book around two decades back), cash money became more common and so did working for cash money instead of laboring to grow your own food, make your own clothes, etc. So labor saving devices shifted a lot of household tasks to women in order to free men up to go get a paid job. This made sense so women could be home with the children since they are the ones that get pregnant and also produce milk.
Men used to pull up the rugs and beat them one or more times per year. Then we invented vacuum cleaners and women took over cleaning the rugs.
Women and men were both often very overworked, but it's possible that the historian couple saw the wife collapse in part because a lot of what we classify as women's work today was handled by male labor at one time and in part because standards of living were generally far lower back then. Trying to maintain anything resembling our current standards without modern labor saving devices is crazy on the face of it. If, on top of that, you expect the woman to do a lot of chores that would have been male labor at one time, yeah, you are going to run someone into the ground.
Back when I used to read such things, studies typically found that women with children were chronically short of sleep whether they had paid jobs outside the home or not. People generally underestimate how much work homemakers are doing. Friends and neighbors routinely demand "favors" because they see a homemaker as someone who has nothing but leisure time on her hands, not someone busy cooking, cleaning, buying groceries, etc all day long.
In my marriage, I also saw evidence that my husband had no real appreciation nor respect for the amount of work I did as a full-time wife and mom. It is one of the reasons we are divorced.
So I'm abundantly familiar with the fact that most of the world underestimates how much work women typically do, dismisses it as "not real work" because you are just supposed to be thrilled to pieces to be home with your children, etc. But the book in question was a serious history book and was remarkably even-handed, which is one of the reasons I mention it relatively frequently. I don't like works that hate on men, that act like women are merely victims of the so-called Patriarchy, etc.