I work with a couple of women who married late (in their fifties), and their resentment of their co-workers with children is palpable (one even asked if they could bring their dogs to a company picnic if other employees were bringing their children).
I suspect these women were just getting married because they didn;t want to age alone; all they do is complain about their husbands (I guess it is hard to teach old dogs new tricks).
Young people today often have no reason to get married because children aren’t part of their future (for various reasons they give). If my wife didn’t want children I wouldn’t have bothered marrying her; the two go hand-in-hand.
I thought I would be going out on a limb, saying marriage is only for the children. And you said it. It's true. If not for children, then it had better be true love that's lasting. If both the man and woman don't want children, then the motive is often financial security and not true love, not a solid foundation for staying together. The people I know who are marrying while old are each financially secure. Others I know who are not, carp about each other.
We got married young; my wife was 21 and I was 23, this after we went steady four years. We were both poor but knew we wanted children. Been together 44 years and enjoy our grandchildren. Best thing was marrying young - and wanting kids.