The late boomers/early X'ers learned a hard lesson. They were taught that they could have it all only to discover when they tried to have children in their mid to late 30s that they were duped.
The younger generation have seen their older sisters and aunts struggle with fertility and have taken heed.
Well, another thing is that bringing children into a Boomer dominated system was not very appealing. We decided to forgo it completely. Those now in their 20s will never have to deal with Boomers running the show, by the time their kids are in high school many of them will be dead.