Sorry I didn't get back to you sooner, Zues, I couldn't type from my phone. I'm in WI, next door. Enjoying spring here very much, especially the lilacs!
A business partnership is rarely 100% financial - and they often fall apart for non-financial reasons. There is a financial aspect to M, and since you can't legislate feelings, they legislated the parts they could - the financials and the possession of the children in case of a breach or contract. Not very long ago, women could be put out from their home and the husband kept the children. The laws were like what you see in the Middle East today. They were eventually changed to protect the women from being so vulnerable.
It is very, very recent that women have been able to support themselves financially, very recent that they had any legal rights, that they weren't chattel (owned) by their fathers, then their husbands. My grandmother was the first generation of women who could vote. Many, many women experienced being looked down upon because they worked - in my lifetime. And the gender gap in pay is still dramatic.
Do the laws need tweaking? Definitely. I think the no-fault concept has gone too far, it shouldn't be the only option.
I think your idea of why men and women marry, is incorrect. Historically, women needed protection and men wanted heirs, and trust me, the women were not so crazy about having all those children - they knew the risk of dying in childbirth, and how it would wear their bodies down. That's why many men were widowed and went through multiple wives because they were simply wore to death.
Also, it was more common to live in extended family groups or tribes where everyone took care of each other. Modern marriage is completely different than it was just a few generations ago.
It has also been a strategic alliance - that's how it became a religious rite - the church wanted in on the power brokering.
Men has always had access to sex if they wanted, there was no reason to marry for that.
The support is usually meant so the W can continue to do her part of the partnership... raise the children. As society evolves, the laws should evolve with it, but there's definitely a lag. Men are increasingly getting shared custody, but that is a completely new thing.
M 16 yrs, WH62, P54 3 adult blended kids EA 11/13, BD1 6/14 PA fall 14, BD2 2/15 Piecing 2015, BD3 12/15 Separated 4/16 WH moved OW in 5/16 Divorced 6/15/17