I think it's similar in a way with obese people, they know the basic idea is to eat less and exercise. Even if it sounds simple in theory, a lot of them struggle with it and some don't even want to do much about it even though they know they expose themselves to health problems.

Most men know what makes a man attractive to women. They know some aspects are out of their control like how tall or how handsome they are. They know that if they were leaner with a six pack and they were to approach more women they could have more casual sex. They know obsessing over one woman is unhealthy but it's what they crave. They also know when they get married, their wife will still find other men sexually attractive and might cheat but they want a family and are willing to accept the risks.

I don't understand why marriage is so unnecessarily risky in the western world. In my country, there is no such thing as alimony, once you get divorced, that's it, you don't owe the other person anything. And when you get married they ask you how you want to share things, you just fill out a form and you can choose to have everything 100% separated (I think it's called "separation of property matrimonial regime"). Marriage is a formal way to recognize a family here, not how to deal with money. When my parents got divorced, they just signed a paper.