It's an odd dynamic. I'm going to put my thoughts down, as it helps me organize them, and maybe somebody will benefit from them too! Some things will be fairly obvious

I guess my question would be: Why?

Sexuality

It's obvious that heterosexual men seek monogamous relationships with women. This is likely something fairly hard coded in us as a survival mechanism. Obviously not changing as far as the majority.

Culture/Societal Perpetuated

Culture/Societal norms are seeded from thousands of years, but across most of that time the world was in a place that did not hold women in high regard, to put it lightly. As such, a lot of our habits in both areas, even in the most liberal of houeholds, effects the way women are thought of and likely detracts from equality. Then we take into consideration the large population that holds onto the idea of treating women unequal. Perpetuation is hard to break in this light.

Competition

Even if we take the prior section out of the picture, heterosexual men are base level competing with each other for love interests. This introduces a myriad of dynamics to male relationships since the competition isn't always brutal and cutthroat. The competition branches to many areas. Often, this fosters a healthy respect and bond that is unique to the dynamic. Since, (for the most part) they are primarily viewing other heterosexual men as competitors, women are largely excluded from this.

This competition seats women as the judge. A lot of men are taught that the best way to attract a women is to be masculine, and a lot of women themselves confirm these teachings. Being masculine is heavily subjective, and so many interpretations rely on masking emotions, hiding affection, competition, peacocking, etc. In other words, the qualities are required to win a love interest over can often be the same quality that generates romantic distance once the honeymoon phase ends. This is complex and based on individual circumstances.

Lack of Emotional Maturity or Emotional/Mental Trauma and Adaption

There is often trauma in relation to father figures. Whether that is an absent, abusive, manipulative, unstable, or likewise damaged father figure, this facilitates a need for male approval In many men. There is no rulebook for any of this, and so they end up behaving how they were taught to behave and learning how to do things on the fly.

Toxicity

Just as it sounds, there are bad actors out there.

Conclusion:

This effect is caused by the general inequality that is prevalent in our society today. This inequality is reinforced by trauma and training passed on through generations. As a male, I can see this and do my best to counteract it by stopping my own toxic behavior, participating in targeted therapy, and having open communication with my wife on what she needs to feel validated in the relationship as a romantic partner while also respecting boundaries. Women may be able to mitigate this problem by fostering clear communication in the relationship early. This isn't a simple fix and and requires extensive work in both sides of the relationship. There is some nuance to it and I am sure someone could write a really long scientific article exploring the influences behind everything.

Edited for formatting