The social role of the stay-at-home mom exists for economic reasons. If one parent makes enough to support their whole family, it’s financially responsible for one parent to do the majority of the household and child-rearing labor, and the other to do the labor that makes paper money. That way, they don’t have to outsource their childcare to daycares until their kid is in kindergarten and to summer camps until they’re mature enough to stay home alone. 

Of course, not all families have enough money to support a stay-at-home mom so that they may outsource some of their childcare to grandparents or other family members. Then again, many mothers are reluctant to leave their careers, as even a brief absence can hinder future growth. It’s a lot more challenging to go back to the workforce after years away from it than people might think. Even simple data entry jobs are not handed out to parents who haven’t worked in 10 years.