In Egypt, for example, the norm is people live in the family home until they're ready to move out and start their own family home. So marriage is quite an important step🪜
Also, the fact that extramarital (→by which I mean without marriage= premarital, not adultery) relations are frowned upon means you normally would marry a person once you feel you want to be together, since there isn't an option to simply live together otherwise 🤷🏻
There are other reasons, but those were just the first to cross my mind as I wondered if marriage still meant anything in the US.
Why would anyone get married in your culture if they could simply just live together, have kids, start a family no questions asked?