There are some deeper and long-term reasons why marriage is a thing in our society.
- First and foremost is the religious aspect, which was a foundational part of Western society since Constantine made Christianity a thing in Rome and the missionaries spread the religion around the world and here in the US. The Bible essentially calls any sexual activity outside of man/woman marriage a sin. Marriage was a religious ceremony to secure the family as one and secure the family unit of the two parents with their children. More people (as a %) believed in these things during the formation of our legal structure, but many still do.
- Secondly, it is a benefit to society to have people in committed relationships to cohabitate and co-parent their children. Society is more stable and it is generally easier to be fiscally responsible when 2 people share the burden. Granted their are cases when none of this applies, but across the broad spectrum of society, the principles are reflected in the data. As such, the government attempted to make marriage a legally beneficial thing and got into the marriage business very early on in American society.
The first aspect will make no sense for a non-Christian (I'm sure other religions could jump in here as well, but this is the predominant one in the US). If you believe in the Bible as God's word, then marriage will continue to be an important part of life. The second aspect is something we may want to change in the near future, but I'm not sure how we would even go about it.
I am a devout believer in Jesus and got married at 22 as a virgin. I wasn't having sex until I was married and she is the only person I have ever even been naked with. 21 years later we are still married. I think the sex is wonderful (although life gets in the way of frequency), but then again, ignorance may be bliss in that regard. Don't care as I'm really happy on that front. I also chose wisely and my wife is a hard worker (she makes more than me this year for the first time in our marriage) and a good mother and stays in good shape and still looks amazing at 44. Additionally, we are polar opposites in a lot of ways and have had a great deal of benefit from learning and growing together. She's pushed me to be a better man in many ways and I've given her self-confidence and gotten her to slow down and enjoy life more often.
I shudder to think of what I would have become had I been left to my own devices. Maybe I would have figured it out, but there would have been a LOT more mistakes along the way. I honestly think I may have ended up in jail or dead by now. I'm a reckless, impulsive, short-tempered thrill seeker inside and it has taken decades of God's hand and my wife's gentle reminders to keep me from going off the rails on multiple occasions.
For me marriage has been an enormous benefit...I didn't even talk about the children aspect yet.