Beating the game of life was tough in 18th century France, with all the obstacles: birth, growing up, marriage, children and making money to survive- your time was limited. Of course the infant mortality rate was higher 200 years ago, but even if a baby survived their first trip into the world, there was only a 45% chance the child would make it to age 10!
The struggle to live didn't stop there, next came marriage. Marriage was a happy time of joining new families and maybe gaining a sweet dowry! But after the knot was tied french couples only had about 15 years of happiness to look forward to. Where marriages today last an average of 30 years, in the 18th century they only lasted about 15 years, and this was not due to divorce!
There were, of course, added risks to women, who gave birth most likely more than once. This lead to many widowers, which in turn led to many stepmothers! What about the stepfathers? Well there weren't many! Only 1 in 10 widows were like 'Lady Susan' the rest remained single.
So was it good for the men to remarry? Not for wife #1's children! When a father remarried, and the new wife had more children of his, the divisions between the parents' assets (think land) was greater, making it harder, or at least a bit more challenging, for the children to continue their adult lives. Times were tough enough as it was! All the stepmothers floating around made the game of life more difficult for the heirs.