Biologically, and that includes psychologically, what these people are doing is not strange. Until very recently in evolutionary terms (like, yesterday afternoon), the 'norm' for human females was to have as many children as they were able to have, either until they die or until the menopause. People who carry on like this are behaving naturally. the more kids you had the more you ensured that your genes carried on. That's what life is ultimately about.
It's the rest of us who have, for good reasons, made a brain adjustment, and some practical changes (using contraception) which mean that we are not behaving in a natural way. It may be a good way we have chosen, but it has yet to become natural in evolutionary terms. It'll take a while.
I've noticed on another thread that the main criticism is about choosing not to use contraception, as if having children was an intrinsically wrong thing to do. It isn't. It's a strange thing to do in our modern culture, perhaps, which doesn't encourage it, but it's not intrinsically wrong or strange. It's just our inherited biology and psyche at work. I guess some people just have a stronger reproductive urge than others.
Big deal. Not.