There are plenty of places today where children are still your social safety net, especially as you go into retirement. We just happen to live in incredibly well-off countries where this need and motivation has largely disappeared (which shows to some degree in our reproductive rates). There's nothing wrong with it - practical reality trumps blind ideals every time.
Even in rich countries, properly equipped children can provide resources that are worth millions if not more. You can't buy the loyalty that a child would have, and a tribe of highly educated, resourceful children is quite a force to have in your old age.
In my experience, the families that had 3 to 5 children, where at least 2 or 3 of them supported each other went far further than others. They save money by being each other's insurance, are able to share resources and knowledge, help each other in rearing their own set of children, and the implicit trust is something that can't be bought.
Of course, it can all go sideways too, but that's applicable in any situation. But the upside is huge.
