Huge numbers of those kids grew up in broken homes, have come not to trust relationships. It's not a natural shift, although it's happened in the past, too, especially near the end of the Roman empire when it became really a pain to try to raise a family because of the economic strictures the later emperors put on economic development...it's a shift away from the future, spawned not by the Xers, and not started by the boomers, although they were involved in it, but by a self-indulgent meme that perculated through a lot of the 20th century that decided a person's right to self-fulfillment meant that they could dump on the backs of their kids, leaving their kids in precarious situations.
Societies with weak family structures and no kids tend to crash when crisis time comes. The future will see if this paradigm holds true this time around.
The truth.
The nuclear family isn't the only possible strong family structure in which children can be raised into happy, self-sufficient, socially responsible adults.