Another obvious reason in these days of sexual revolution:
Why would you buy the cow if you get the milk for free?
I was talking to some older men a while back. They told me that back in their day, they were eager to get married, in part, so that they would get to have sex.
The sex revolution has upset the dynamic of male/female interactions, in my opinion, as has contributed to lower rates of marriage, and people getting married at higher ages.
There is another dynamic I think is being ignored.
Most millenials are flocking to the urban centers. There “seems” to be so much opportunity for careers, multiple partners, and a vast world that never ends.
Wanting to live outside a city, even in a suburb, and raise a family is just not their life-time goals. They want to be hip, live in the city, and be a hipster. Being married in a small town or suburb is just so NOT cool.