The longer you live together and pool resources the harder it will be to cleanly break apart. Marriage makes an implicit contract and ruleset an explicit one. If you are gonna be in a perma-relationship, why reinvent the wheel when you can adopt an existing system that has been in place in one form or other for thousands of years?

I thought marriage was about love, but if it ends up being about managing resources then why not start something like a company with equal(or not) shares, vesting periods, etc? It would make more sense to me because it's a more efficient way of dealing with shared assets than the current legal form of marriage.

Sure, think of marriage as a default, off-the-shelf standard contract which attempts to make sure neither party is aggrieved if a split happens.

You can of course use a non-standard contract. It's called a pre-nup, and it has both the downsides and upsides of a non-standard contract.

Marriage being "about love" is a relatively recent phenomenon. It has previously been about managing resources, making family political/social alliances, and (as it still is) creating social and economic stability for children.

I don't have, want, or even particularly like children, and even I have a problem thinking of them as "shares" or "assets" or pre-deciding their fate with a formal contract written before they were born or old enough to express their own wishes.

Because every couple is different. Marriage is incredibly simple. The actual complexities of marriage don't come from marriage itself but from all the shit left undefined, which has to worked out ad-hoc per couple.

I'm sure if you were the dictator and God-King of a small country, where you could reinvent society as you wish, you might be able to create something that would fit 99% of the population, since you would be able to forcibly squeeze the behavior of each couple into a few standardized containers with corresponding legal rulesets.

Because people who are in love want to get married, like their parents and grandparents and great-grandparents and great-great-parents and [etc] did, not "start something like company for the holding of joint assets".

Getting married is romantic and irrational, and that's why we enjoy doing it.

Contracts are for when a relationship breaks down, not the other way around. The "contracts" offer protections to parents offering a legal path for enforcing access to their children as well as financial protections.

It also seems to offer access to additional social and cultural collateral than just cohabitation and has several inferred expectations in various social spheres.

Parties in a relationship sometimes have wildly different experiences, expectations and motivations "in love" and marriage provides a way to reduce this complexity.

There aren't many things that test your will and resolve more than having to sign a big contract on something. What people will commit to verbally is often vastly different to what they will actually sign to when it's in writing.

I like my marriage to be a bit more permanent than my job. I work in an at-will situation. I can leave anytime and they can fire me anytime, no reason required. That is fine for work, but I like more stability in my personal life. I don't have an issue with a "contract" to agree not to shop around for a better gig. I don't have an issue with a contract that will take a bit of work to undo if it is wrong - all the better reason to get it right before entering into it. Marriage or not - throw kids into the mix and you have one of the big reasons people stick together when maybe they otherwise wouldn't.

Marriage is much more than believing in "love". Marriage can remind you that you might want to stick around even on the bad days. Life isn't always easy, but sometimes it is too easy to walk away from something that is better held on to.

Perhaps as a way of encouraging you to persist through minor stumbles? As a tribute to your partner who dreams/hopes of a wedding?