I’m generally curious why people get married beyond the “because I love them” when it costs so much money.

Getting married doesn’t have to cost virtually anything. Really just the application fee to get a marriage license. The specific price will vary by state, and even by county (within the US, not sure how it works outside). Where I live, you can go to a courthouse and get married for $35.

If you plan to have kids, there are a lot of legal reasons why it’s just a lot simpler to have kids. The same applies without them, to a lesser degree, but with kids it’s just so much more of a hassle to not be married.

You’re right that you can achieve most (maybe even all?) legal benefits of marriage through trusts, wills, etc. But that’s a hell of a lot more work, and the lawyer fees, filing fees, and application fees are almost certainly going to cost you more than a cheap courthouse marriage. Not to mention the added work for yourself.

Beyond all that, though, the single biggest reason I wanted to get married and have a wedding with lots of friends and family was to stand up in front of everyone and profess my love for my (now) wife, let her do the same for me, then have big party with all our friends and family to celebrate it. There’s nothing wrong with spending money to throw a party for something you want to celebrate.