There are probably two major reasons behind this.
1) It is far too easy for people to get married.
2) It is nearly as easy to get divorced. A lot of people go into it thinking that they will be together forever, but I'm sure just as many believe that it won't matter as much because they can get out of it and might just be using it for getting citizenship, or because they got pregnant, or to save money on something... the options are endless.
I would not enter into a marriage with someone unless I felt as though they were as committed to the relationship as myself. There must be a mental, physical and spiritual connection in addition to having some similar interests and goals. While I agree that sex is usually important to both people, I do not believe that it is the glue that cements or holds the marriage together.
Marriage is a lot of hard work and is not something that a person should rush into or take lightly. Be kind to others and treat them as you wish they would treat you. Do not get married, if you are too lazy to be committed to your partner and your family. Be willing to give 100% each and every day. If you are unable to do this, you know what to do.