Ultimately it is the woman making these choices and in advanced societies, women have other options. In hard economic times, couples save for their own security first before considering having children. In the fifties and sixties in the U.S., taxes were relatively low and jobs were plentiful, so women could afford to stay home with the kids. Another consideration, a culture needs men who will make a commitment to the family, or the woman will not make a commitment to bring his children into the world.
Gi's came home...the GI bill was going strong...men could get jobs in plants..and with the plants rolling, people making money, people wanted to have children...it was a sign of prosperity...
and the Church....Catholic churches were full and having big families was the ideal....
my mother tells the story that the local priest would notice if you had an empty year or two...as in , what happened here?...no baby?...
it was a happy time...lots of optimism...
I don't think there is optimism today with the young people...