Why make a commitment to begin with if that's the way you want to live your life?
Because what one couple commits to may not be what another couple commits to.
This whole argument presumes a very modern Western concept of what marriage is truly about. In most parts of the world, and in the West up until about 150 years ago, marriage is primarily a business arrangement, designed for the begetting of children and the management of inherited property. It was firmly based on a quid pro quo arrangement between the parties, and it was not about love, but about security, in the preservation of one's person and the preservation of a family's net worth. The Romantic notion of marriage (with a capital R) is a fairly novel concept.
My grandparents had an arranged marriage. They didn't love one another, in fact, they barely tolerated one another, but they had 9 children together. That was the contract: he got sex when he wanted it and children to help work the farm and to inherit it from him, and she got a secure life with her own household to control, and children to take care of her in her old age. Divorce was not legal in their country at the time, and was also against their religion, but they didn't regret their marriage: they got out of it what they had expected to get when they entered into it. My grandfather was a shy man who was rather pious as well, so I doubt that he sought sex outside of marriage, but if he had, my grandmother would not have minded as long as he didn't a) spend too much money on that pursuit, b) catch any diseases from it, and c) embarrass her publicly. For women, infidelity carried a higher risk because a large part of the contract was that she was obliged to provide her husband with heirs of his body, not (as the old saying goes) cuckoos in the family nest.
Historically, the more wealth at stake, the more dominant the contractual nature of marriage was. Aristocrats commonly established separate households once they had sufficient male heirs to ibe reasonably sure that the family property would remain in the paternal line. However, poor people depended on the contract as well. Daughters were expensive to feed and house, but generally did not have much potential to generate actual money via their labor. Their best value was as a provider of children and in the potential to bring money into the family via marriage.
And I suspect some kids pick up a lot more than their parents would like to think they do.
