More that young(er) folks could afford to live on a single income for the pre-school years. Or, I guess, that there's extensive parental leave and support for the parent doing primary caregiver.
But even if everything was "easy and perfect" (arguably some other countries have this) - you still have something that is generally discouraging people from having kids.
The median Amish family income is about $65,000 and typically has six to eight children.