Why marriage tend to be monogamous?

Well, there are about the same number of males to females.

That seems like a pairing.

However, males want as many females as possible. Women prefer the best genes measurable by wealth.

Some restaurants, for example, are full. Some restaurants are empty.

There is no restriction that all restaurants deserve the same number of customers?

So why monogamy becomes the norm?

Look at the Arab. The oil money goes to the Arab king. Why? Because the Arab king is in power.

Is marriage good for women?

Many people want to prohibit prostitution and porn. They said those are so bad that they have to be prohibited.

So, if a woman wants to have sex, what’s the alternative for that? Marriage.

By prohibiting the alternatives, societies pretty much push people into marriage.