You can have kids with a partner, but really no reason to formalize it with “marriage”. I guess there are tax reasons though that make it more logical though.
Like it or not, the government unfairly taxes single people.
But if nothing else, marriage is an agreement that you’re not just gonna nope out when there’s adversity or when something better comes along. It’s a powerful mutual gesture.
If you aren’t compelled by that idea, there’s someone out there who will. Maybe you have to dump your current 6-year-long situationship to go look for them, but hey, it’s not like you’re married. ;)
But there are also subtle but real and pervasive social & community benefits to it. You are often perceived by default as "established," reliable, trustworthy when you are married, in ways you wouldn't be in an unmarried partnership.
"Just a construct of society?" Sure. So is money. Something being a social construct doesn't mean it's fake, or powerless.
This has zero legal binding whatsoever while having exit clauses that statistically heavily favor women even in cases where they are the ones initiating. While it may make sense on a case by case basis, its a statistically terrible decision to bet on
Source: A 40-year old who has no interest in marriage and only saw it as an "antiquated social construct" when I was younger. I learned there's more to it.