Another reason for not getting married, this is pretty deep, but;
It's an extremely big commitment. As human, naturally we want change eventually. I'm not saying this is for everyone, but people who get married, and have been together for a long time can often become unhappy. They may get bored with the person, or even find it difficult to live with them as their habits start to become a financial burden etc. If they do get bored or are arguing with the person, they will file for divorce and probably marry again. What I personally find better would be to be in a relationship, but again I'm not saying that people who do get married are stupid, it's your choice. If you're in a relationship with someone, if it's long term, and eventually you start becoming unhappy, you can just end the relationship. Whereas, if you're married, you have to go through dividing assets unless you have a prenup, but even then it can be quite difficult, especially if you have kids. Personally, I would like to go through my life, where I was happy for moments in time, with different people, rather than take the risk of getting married and eventually becoming unhappy, but staying in the marriage to avoid hardship. I think this is okay if you don't have or want kids, which is my choice, but I don't think that lifestyle would be suitable for a child.