The more kids you have the more likely it is that some are going to strike out on their own to alleviate the burden on their parents or they stay and contribute to the household.
Another point if I might. As so many single women are raising kids, it seems to me that there would be some what less desire to kick the kids out of the nest. When that happens then mom is alone. Most people don't like to be alone.
I see your point about the single Mom’s. We are an intact family, but we are in process of building a modest home around us, it is unfinished as we live in it, and my husband works but has some health issues and so my son’s are helping with that as well. I’m having difficulty finding a job right now, hence the working together to keep this ship sailing.