500 years ago, "until death do you part" probibly meant about 20 years, which with a lifespan of maybe 40 years, was just enough time to raise a kid, secure the villiage farm and die. Marriage was required and squeezed into life, I suppose.
Today, even though you have more and more people waiting until their 20's to marry, which is maybe 5-10 years older then historically, people are living 40-50 years longer. So you have this trend where people aren't waiting all that much longer to get married than they would have historically, while lifespan is in comparison growing exponentially, making "until death do you part" a commitment that is getting longer and longer and longer. . .
Relatively speaking, even if you wait until you're 25 to get married, you're still getting married young. The way modern society allows a person to live without the requirement of marriage and children is starting to make marriage a thing of tradition & desire more so than anything else.
As much as I believe feminists and governemnt aren't helping the cause, I think the major thorn in modern marriage is the decreasing need for it coupled with the increasing time it has to survive in a much different society.
It's just getting harder and harder, the benefits of it aren't really increasing and the downside is harsh. In my mind, it's becoming more and more like an undiversified, high risk stock portfolio that you promiose to love & cherish "until bankruptcy do you part".