That's a bit, certainly. A larger component is The Key: Humans are optimized to live in hamlets of 50-100 people, where child-rearing duties are frequently shared across multiple households. Modern society atomized extended and then nuclear families, increasing the child-rearing burden on each individual mother in a distributed fashion, because modern society is ironically both hyper-dense and also hyper-isolating. The modern motherhood model is "pioneer woman" with no community-shared burden, due to lack of extended community/clan childcare system that was present 100+ years ago [in successful communities]. Fewer grandparents, fewer aunties, fewer cousins in our atomized society implies more impersonal private or gov day care / school care, or burden directly on the mother and mother alone. Motherhood is more difficult with reduced opportunities for "distributed" child support.