Increasing obesity is also a significant factor. "At the wedding-feast the least eater is the bride." - Spanish proverb
Remember when a woman over 30 who wasn’t married was called an “Old Maid”?
The stigma of being unmarried went away a long time ago.
Also, it used to be that eventually a guy ran out of buddies who weren’t married, so you couldn’t just go out with the boys anymore, so there was no choice but to get married or be considered a laughingstock.
Again the stigma of not being married isn’t what it used to be.