I agree so that marriage is, also historically, as much about economics as it is about love.
Still, I think what's helping ensure commitment in that case are the children, rather than the marriage. It's much easier for a married childless couple to split up than for an unmarried couple that has children.
I would argue exactly the other way around: A lasting marriage is not itself the goal (though certainly nice to grow old together), but serves the purpose of raising offspring - that's what counts for every species that has survived.
This is the luxury belief. It feels true, it doesn’t conflict with secular values, but all the research points to it being false…
- In-laws - you become a member of a new family, new levels of mutual privileges and responsibilities
- Public wedding - Proclamation to both social circles that the new family project now has officially started
- Family name - new Identity
- ...
Really, most couples I know really only marry when they are already very well established in each-others circles, as sort of a affirmation of their love. Maybe this is also because legally you can achieve the same protections for your children a lot simpler than getting married.
But this doesn't mean the whole of the Netherlands works like that, just my social circles :)
Still, I would argue this:
Lets say your 19 year old daughter wants to introduce her boyfriend of same age into your family.
How would you rate her (and his!) seriousness if
a) they lived in his apartment or
b) they are organizing their wedding.
I would wager b) would be "well-established" much quicker, especially in the wider circles, and thus have more "social resources" sooner, thus giving their potential offspring better chances. Of course, with kids out of the picture, it wouldn't make much difference. But that is exactly my point: Marriage serves having children.
Your "(a) living together" is a much more serious and well established relationship than "planning wedding".
"living together" implies a de-facto relationship with the legal protections that brings. "Planning a wedding" gives none of that.
To your point: legal protection is a very serious "social resource" given potential offspring a benefit.
The data show that married-before-cohabitating situations have more robust relationships for raising children.
In many US families, it's not uncommon to take people you're seriously dating on family vacations, or have them over for holidays, etc.
Some people who choose not to get legally married have a ceremony and/or party.
Some people who get married don't change their name. People who don't get married can change their name if they want to.
As soon as couples start to have concrete plans for children (or children are already on their way), marriage suddenly becomes very relevant for many relationships, and is often demanded by at least one side of the partnership.
This puts aside the romanticised view of marriage (which might be perceived equivalent to living together) and points to a more fundamental reason for marriage: Securing resources for your offspring. And offspring needs a lot of resources for a long time.
In the end, its commitment that counts. And marriage was built for ensuring commitment as much as humanly possible, with a high barrier for abandoning.