When you work 8 hours a day, have 1 hour lunch break, waste 2 hours commuting, to earn barely enough of what Adam Smith considers ideal (twice the cost of living), it’s hard to sustain a second person, much less a third that requires near constant monitoring for over 7 years.
From a pure economic perspective, a child is a total money sink for at least 18 years. In many places (mostly urban), it’s simply not viable to have one.