I would submit that the answer to these types of questions begs a deeper look. I think people get caught up with the ideology of M, which is strictly a social construct.
If we were to go waaaaaaaayyy back, to a time when our very existence and survival was dependent on social bonding, coupling was more of a life long endeavour.
While at least SOME of us are still driven by that deep seeded, instinctual NEED, it is no longer necessary for human survival. One could potentially theorize that, if we catered to darwinistic thinking, this type of behaviour, of becoming disinterested in or even resistant to lifelong coupling, could be a natural evolution to normalize, or even reduce our population.
I would speculate that, if we were to take a small group of people and placed them on some other planet capable of sustaining human life, there would be a strong, instinctual drive to couple for life, once again.
If one leaned more towards theological favour, then there must be some learning that people and society need to learn from this change or apparent degradation of the sanctity of marriage. Is it truly for us to fight or resist what has been handed to us or is it for us to learn humility and compassion and strengthen our faith?
I think that all we can ever really do is, the best we can do and always strive to do better. That includes trying to make the best of a situation that is traumatic and be conscientious of the messages we show and pass on to our children, through these life changing events.
