Why do married men make 44% more than single men?
econlib.org
econlib.org
This is especially true if you have children, who need eyes and hands nearby at all times when they're very small, and need transportation and enriching activities such as vacations with their whole family when they get older. You seldom can split that time up between partners in a satisfactory way.
Married men negotiate their salaries with more skill than unmarried men. Marriage is often associated with the wish to raise children. Children are expensive. Therefore there's more to lose if you don't negotiate your salary well.
Age is conspicuously absent from the controls
Two CAN NOT live as cheaply as one, no matter what the old proverbs say.