because what is there for them to gain from staying married? its often quoted but its largely been proven true - married men are happier then single men.. but single women are happier than married woman. (post honeymoon period)
Look at it sociologically, and in the scheme of history.
Why did women get married for thousands of years? Across multiple independent societies? It wasn't to be happy.
They did it because for most of human history it was a necessity for both their own survival and for the survival of their children. They needed a husband because a husband provided protection, resources, the ability to provide off-spring, and elderly care.
Marriage in the past was a very practical transaction. Both sides - men and women received great practical benefits to their lives and futures, and both ended up hugely better off materially and circumstantially than their single counter-parts. This is also why the idea that marriage was 'oppressive' to women is a bit wrong. Its partly right in the legal-possession sense.. but its wrong in that it was all for men at the exploitation of women. It was incredibly mutually beneficial for both parties.
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Fast forward to the 20th century.. and marriage is in crisis - especially on the female side. Why? And why less so for men?
Look at what women get out of marriage today..
Security - we live in the safest societies in human history.. you don't need a husband for this
Prosperity - you can work
Having children - still true
Elderly care - NHS/pensions/savings
Only one of the 4 key reasons to get married is still true (hence why divorce rates are low after childbirth but peak again as the kids age, and the man isn't needed any more)
What about the man
Childbirth - still true
Regular source of sexual satisfaction - largely still true
Status symbol - largely still true
Maintaining the house/cooking - on average still true
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Its pretty clear that men still get far more of the initial sociological bargain than women do..
The most damaging thing though is the newest addition: 'Happiness'
Happiness is what's been sold to women as a replacement for the piratical benefits of marriage. Its the reason marriage rates are still high.. despite all of the bennifits disapearing over time. Because countless media sources have sold women on the romance.. that marriage will make their life happy, and give them fullfillment.
It doesn't.
Marriage is a pratical change of cirumstances - it doesn't make you happy. You make you happy. A positive person with a decent mentality will be happy in or out of a relationship, and a misserable negative person will be just as misserable when married. Even for a positive person, a marriage will not ALWAYS make them happy, and there will be times of prolonged sadness throughout their marriage.
So, understanding the above, what happens today is simple:
- Men and women are sold the idea that marriage is meaning and happiness...
- Some point after the honeymoon period they realise this isn't true...
- For the men, they still see a good few practical bennifits, so they stick it out
- For the women, unless young children are involved, they see very few practical benifits, so they feel trapped.. in a situation that is not delivering them the happiness they were promised, or the practical bennifits that would make it worthwhile when unhappy..
So they want out.