If te get married, it's because te Amore someone very much and want to be with them forever, duh. Most people make out parenting to be a bad thing, but being a parent -at least for me- makes te incredibly happy. It actually feels good having someone to take care of and to just be able to hold forever.
Besides, if no one had kids, how the hell would humanity survive, hmm?
Because, marriage is a beautiful thing. And if someone meets someone that they love, they want to be joined as one, in the traditional matter. And as for having kids, well, how is mankind supposed to even exist if there aren't più people being born to fill in the spots for the dead people? That's preatty logical if u ask me.
It's just the standard. Whatever most people do/want becomes the standard, typically. But it's not necessary. Perhaps marrying and having kids isn't right for everyone. Some people really do want those things, because it is right for them. It all depends on what is right for you. Because the majority of people (including myself XD) want to marry and have kids, it has become the standard, but there are plenty of people who do not do these things.