The range of culprits is quite large.
Some blame widening U.S. income and wealth inequality. Others point the finger at the fall in religious adherence or cite the increase in education and income of women, making women choosier about whom to marry. Still others focus on rising student debt and rising housing costs, forcing people to put off marriage. Finally some believe marriage is simply an old, outdated tradition that is no longer necessary.
But given that this is a trend happening across the globe in a wide variety of countries with very different income, religious adherence, education and social factors, it’s hard to pin the blame on just a single culprit.