I think that the stigma of premarital sex and having babies out of wedlock has declined so much that marriage is now for people who are religious or otherwise serious and therefore more likely to marry well and to work problems out in order to avoid divorce.
So how often do unmarried couples who have biological children together eventually split up?
My husband’s parents divorced in the 70s, and it devastated him. He does not want to go through that, and he really does not want to put his kids through it.
Of course, his brother and sister are both divorced, so that’s not the case for every kid of divorced parents.