The rent is too damn high
It takes longer into adulthood to achieve stability
Porn brain
Phone brain (24/7 infinite entertainment)
Dating apps are not delightful
The pandemic led some people to stay in for good
Loss of third places (rent too damn high again)
Tight job markets lead to reluctance to bring kids into the picture
Healthcare is more expensive every year
American individualism diminishes multi generational family support structures after a generation
A long tail of other causes: drugs, gun violence, obesity, losing one's religion, growing up with divorced parents