Marriage has been an institution in flux for centuries, but the rate of change accelerated after California Governor Ronald Reagan signed the revolutionary Family Law Act of 1969, retroactively abolishing the “traditional” binding contract of marriage and replacing it with no-fault divorce. The feminist revolutions which followed forced further changes in marriage. The result (not predicted by experts): a large fraction of women valued their independence more than their husbands.
A common pattern has emerged for women. Marry, have kids (with a husband helping raise them during those early difficult years), divorce after they’re in school, and collect child support. This gets the children she wants without the bother of having a husband (after some years of marriage). The resulting high divorce rate — over 50% — with roughly 80% initiated by wives, makes marriage a risky proposition for men.
The numbers tell the tale. In 2005/06 less 60% of US adolescents (11, 13, and 15 years old) lived with both birth parents, per the OCED Family Database (source). That was the lowest level among OECD nations. That number is probably lower today. The numbers are worse among the poor and some minorities.