[fastball]

That's because it's not merely a cultural issue, it's a biological one.

By necessity, all women that have children need to take time off, at least in the pregnancy/birth stage. The productivity lost is generally less if you only need to coordinate one person taking maternal/paternal leave. So the obvious choice is to extend the leave of the person that absolutely must take it.

[User23]

Breastfeeding is also a major issue. For the first six months of life it's far and away the preferred food source. And breastfeeding infants need to eat every 1-3 hours. Sure, women can pump, but then they have to do that every 1-3 hours to maintain their supply. Also while pumped human milk is better than formula, it's still not as good as direct.

Biologically speaking pregnancy, birth, and raising children makes serious demands on women that it doesn't on men. Treating people justly requires recognizing these differences.

[rabboRubble]

And by necessity, some men take over primary parental responsibilities when their child's birth mother die in child birth or decide wifehood and mommyhood isn't for them and run off.

[aaomidi]

It's both actually. Different cultures have had different approaches to raising a child.

Painting it as black and white doesn't help.

[Pfhreak]

The phrase 'not merely' implies 'both'.

[aaomidi]

Sorry missed this.