It has been traditionally expected that two people will date and eventually marry if the relationship works out. Modern couples have taken a long look at marriage. Many of them believe it is an institution that has outlived its time. They see marriage less of a guarantee of long term commitment. To these couples, marriage is nothing more than a dangerous trap that allows people to relax too much.
Traditional marriages have often been relationships where two people have ended up despising each other. Because society expected them to stay together no matter what happened, they did so. Their happiness was not personal. Happiness was achieved by being part of their society as a couple. Modern couples believe happiness is attained only with hard work, and that being married robs a relationship of this effort. They would rather defy tradition and keep their relationship on an informal basis.