People aren't easily replaceable...especially high talent individuals. It's also a big burden for an organization to pay for non-productive workers. And if someone has several children in a row...then what? What are the limits?
That's absolutely true, but hopefully the government (or social security) pays for it. Same as for medical leave (in Slovenia, only after 30 days though - first month is paid by the employer). That way, the government is supporting entrepreneurship and small businesses, which would otherwise be disproportionally affected by a single person leaving (in a big company, the law of large numbers makes it easy to predict, and therefore manage, absences).