The old societal model was:
A young woman would trade her youth and fertility exclusively to only one man, and he in turn would be the workhorse and take care of her when she gets past her prime. This was a great incentive for men to work, become men, and get married. You got a prize, a young beautiful loyal wife. In theory, as we know life isn't perfect. She does him a favor early on by being a virgin/exclusive and later he does her a favor by staying and supporting her instead of leaving her for a younger woman. They both get a prize.