People marry to get company that they would not get if they were single. Nobody wants to return to an empty home, which is what happens if you do not marry. Isolation can be killing. Studies have shown that isolation can be harmful to health as heavy smoking or drinking.
It is only in the movies that bachelors look young and carefree. If you see men who are single, after the age of 28 or so, you will find that they look older and more worn out than married persons of the same age. Scores of studies done in North America and Western Europe shows that married people enjoy better health than singles. They also live longer.