Marriage is a like a contract, or a way of saying you swore to be with that person for the rest of your life,
Getting married means you're taking said person as your family rather than some girl/boy you fucked last night at the hotel down the street
Some might say its a way of taking responsibility and some say it's not something important in life
While later you'll realize not having a kid means you basically just ended your entire blood line and just threw away all the hardship your ancestors and parents blood and sweat that they used to grow the family
Yep. With girlfriend/boyfriend, a "let's break up" will shatter the whole relationship right there.
But when you marry... Well, since it's complicated and very restricting, two person are more likely to be tied for REAL. If both party are devoted to their relationship, of course.
Tbh, in this day and age, society doesn't really consider marriage to be 'sacred' anymore except for some 'religious' societies. It's fine. But even so, i think having a well-thought marriage is better than switching partners left and right.