Part of the issue is that they spend a lot of disposable income on disposable expense, but consider it absolute necessities. They can't imagine being willing to cut $10,000 a year on alcohol and night-life, while having a kid, let alone 10. They don't realize that being a parent will change their interests, or worse: are afraid it will.

Then when they turn 40 they start writing articles at Buzzfeed about how glad they are they didn't have children, and never will. (They're not glad).