Marriage is a concept that is bulletproofed by thousands of years of human history.
New way of life & temporary bonding (mostly single life & multiple sexual partners or loose relationships) was not common before (only in some primitive societies) and sleeping around was permitted mostly for high-profile men in positions of power (and even then it was usually treated as secret by them). Even in Greco-Roman world, sexual freedom was perceived as something temporary while family came always first (together with all the responsibilities), there was "fun period" but ultimately everyone knew that serious duties & marriage will happen.
It is easy to look at marriage while being jaded or single & childless & not married before as something without sense, however marriage was conceived mostly as a "stable cell" for raising children and building society on solid foundations (as married men were less of "loose cannons", they were also more obedient when it came to observing rules of power and they were more eager to gave their own lives in defending their families, children, land given by king, prince or warlord if man was supposed to be a soldier in time of war). For me it is clear that non-married guys and childless guys will never fully comprehend how having a family change your way of thinking - suddenly you want to work more, don't want to lose time on futile hobbies or relationships anymore, you think how to protect your family from various threats if you need to, you are less interested in making aggressive manouvers at work that are not well-thought but simultaneously you plan for the future more and strategize more about important choices. Sex becomes less important as marriage provides you with it often enough to stop thinking about it all the time and it becomes natural that you think about other matters, which are more important. Some of my old friends (peaceful guys) trained themselves to use guns and acquired gun permits while declared themselves as pacifists years before they had little children.
Having family puts you into next step of your own evolution - which is incredibly funny as nowadays society tells you that "you don't need to have family, self-development is just as much important" - yeah, well, tbh I do not see too much self-development when I look at single acquaintances of mine or my wife - it's just another boyfriend/girlfriend, another cool trip abroad sort of story or money invested into some real estate (which is pretty much what everyone does to some extent in Central Europe where I live). Being mature is also about understanding that your life and yourself are not constant - you change and having stable family helps you mature and understand other aspects of life better (especially human bonds as suddenly you need to protect them more - it is not only your choice but also your duty when you have children - it changes your perspective a lot, trust me - I still remember how I thought 10 years ago when I just wanted to sleep with many women, preferably with no ties attached and rolled my eyes when I heard that one or another of my friends got married.
Sure some guys hate additional duties, little children cry or nagging of wife (which needs to care much more about baby than about herself - not to mention husband) more than to see value in that higher purpose that is achieved by staying with the same women and raising children but I have already written on the forums that life is not about pick up per se - meeting various women is awesome stage of man's life when you are usually young and everything feels so unique and fresh, there's new experience around every corner, that's how you feel and that's ok, that's how it should be - after some time your own mind usually blunts this need for novelty - that's the call of nature and sign of passing time, getting older - suddenly stability does not sound that bad - it is important to choose the right partner before trying to trick the nature in her own game will end with nature tricking you and idea of marriage supports that need to have family, which most of the people still have.
I generally do not believe that modern tendencies in social bonds will stand the test of time - history is full of periods of opressive conservatism and waves of liberalism in personal freedoms (including sexual freedoms), I would say we are currently during the peak stage of liberal wave but raise of conservative tendencies in the last couple of years was strong. The change will probably be visible in the next twenty or thirty years in order to secure the pillars of developed society.
