Various studies have proved that it is difficult for men to remain monogamous.They cannot stick to only one woman for their whole life. At one point or the other, they have to have another relationship. Monogamy is not preferred by about 80% of men. They have desire to be with different women.
I think it is a scientific reason..and proved that men can’t control their body urges. Men can't have self-control capacity like women. So if their case of love or girlfriend or crawling with other or in tension and depression they take wrong decision many times. So not all men but has problems that cannot be monogamous.