It's a longer term trend than even the "sexual revolution". My grandparents generation had plenty of families with 5-10 kids. My parents generation had 2.5 kid

It's a longer term trend than even the "sexual revolution". My grandparents generation had plenty of families with 5-10 kids. My parents generation had 2.5 kids, mostly in their mid to late 20s. My generation will maybe start thinking about kids at 30. You could maybe argue that women in the workforce is a social change that contributed to this, as one thing that did change at the beginning of this trend, but surely this as much a fault of the incentives of capitalism turning "Women can work now" to "All working age adults must work, no more stay-at-home parents". Casual relationships, LGBT acceptance, etc. are much later than this trend starting.