All cultures have something like marriage. It's something that will never go away. Biologically, men unfortunately have so-called "first abandoner advantage" (evolutionary psychology speaks of this): men unfortunately can run away from a woman they have impregnated, and do the deadbeat-Dad thing. Then to make matters worse, kids can grow up very maladjusted psychologically, if the mother does a bad job of rearing the baby. There was a controversial and infamous psychology experiment about the effects of bad mothering, by Harlow.
https://www.simplypsychology.org/harlow-monkey.html
A great book on these sort of developmental problems in human babies is "What Happened to You", by Winfrey and Perry.
In a conservative, traditional setting (with no pre-marital sex), sex is just about come exploding out the gates, starting on the honeymoon, so powerful commitment attestation (you know, marriage) is a bulwark against "first abandoner advantage", harlow-monkey-style childen etc, which might otherwise follow the impregnation which is fairly likely to happen next. So marriage can be said to be functionally all about making strong public attestations - at tremendous effort and cost - which will hopefully avoid this automatic, egregious psychological damage if the parents are really bad parents.
This commitment attestation can't be powerful enough. There is also the so-called "7-year itch", which besets virtually all couples. So over time, we shouldn't be surprised to see the marriages getting more and more expensive, and lavish. The bigger the better; the stronger the public statement made, about commitment. Small fortunes are spent on wedding rings, dresses, hell rentals, DJs, professional photographers (even when smartphone cameras are awesome these days), etc. The wedding ring must be an expensive diamond. Wage savings measured in half-years are expected by every one of these modern-day wife-queens, to pay for such a worthy diamond ring. Not one of those still ultra-hard, cheaper Moissanite rings, which can also scratch glass, and act as a symbol meaning "this one is mine, back off", to deter competing horny men who want one's wife for themselves. The symbol of commitment just wouldn't be as powerful, you see.
Then economic downturns come. Oh no, who can afford a marriage anymore? All the rituals and symbols and lavish ceremonies were predicated on waterfalls worth of cash being readily available to satisfy the wife-queens that a sufficient commitment was attested to, assuring them that "first abandoner advantage" wouldn't happen to them.
That's why no one wants to get married any longer.
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"Life is not a problem to be solved, but a reality to be experienced." - Soren Kierkegaard