Or people grew up watching their parents regret starting one too soon and want to avoid that mistake.
People who talk about women being more selective makes me wonder if there's an ulterior motive to choosing that hypothesis. Sour grapes?
There's much more economic uncertainty for the average family as a result of two things.
1. Corporations innovating the labor market and successfully squeezing increasing amounts of wealth out of the workforce: successful union busting, ever more cleverly exploitative labor contracts, the gig economy, unpredictable scheduling, metrics and surveillance, etc.
2. Fewer funds proportionally available to labor thanks to increasing wealth capture by a tiny minority.
It's not only expensive, but it's statistically difficult to overcome the uncertainty and establish a homestead you can believe will prove stable over a kid-raising time frame.
It's easy to understand why people are hesitant to start families in such family-unfriendly economic conditions.
Sexually speaking, the rich get richer and the poor get poorer.