
Love is the number one reason. It's not a requirement that married couples need to have kids. In fact, many couples can't physically have kids.
Also, there are a lot of legal and medical benefits to being married. If you don't have medical insurance or your insurance sucks and your spouse has great medical insurance that covers their family as well then being married means you'll have their medical insurance.
Also being married means they're your next of kin, meaning if you get into any medical or legal troubles, they're the ones that'll be notified first and they'll be the ones to make decisions for you if you are unable to. This benefits couples who don't live with their parents or siblings. After all, if you haben't seen your parents/siblings for years or only see them occasionally, you don't want them making medical/legal decisions for you. They don't know how your life is and most likely don't know how you want these situations handled for you and its unfair to your spouse who is literally sharing your life. It also comes in handy when one or both spouses come from abusive or less ideal families. If they aren't married, the abusive parents or siblings or extended family can shut the boyfriend/girlfriend out of any medical or legal decisions because they are next of kin and take absolute control of their lives. But if they were married, the spouse, by law, has the power to protect their lover from anyone trying to take advantage.
There's also tax benefits but I'm not married so I don't know much about that. And depending on which country you're in, if your spouse grts arrested, they can't force you testify against them.
Also, if your spouse suddenly dies and they have assets or wealth but don't have a will, you are the rightful inheritor of their stuff because you're married. If you weren't married, everything that was bought in your boyfriend/girlfriend's name (house/car/apartment/etc.) and their bank accounts will go to their parents or siblings. You get nothing unless they're willing to share or your spouse has a will written specifically saying you are to inherit his/her wealth and assets. But this law is also dependent on country and some countries recognize domestic unions as proxy-marriages but their family can still sue or file for your lover's wealth and assets to be given to them instead of you and they'll probably get it because you weren't legally married.
Heyyyyy izz okay if people dont get to have kids yk like let them beee iz not even your family to begin withh aarrghh why do society normalize having a kid in a couple a must??? I wanna chop their brains out hnnng...ANYWAYYY I LUV THIS DIZZZZ