Marriage for some is a public declaration of love, for others its a financial contract and for others its both.
By law, it's a contract that brings the state into the relationship to a greater extent, affecting one's legal and financial rights and responsibilities. My feelings on marriage doesn't affect that it's how I was able to immigrate, that it meant when my spouse and I went through university at different times we got additional money -- our choice to marry set up and has had ripple effects through our entire adult lives in very practical ways no matter how either of us felt.
The government incentivizes marriage through the legal and financial rights it gives based on it, though there are also disincentives in the related responsibilities depending on one's position. It's questionable how much they should do that. My oldest wouldn't even have British citizenship if his father and I hadn't married as he was born at a time where a British father could only pass on his citizenship if married to a non-British mother. That's had issues which is why the law has changed, but it doesn't change that many people are still impacted by the law using marriage as a functional tool to decide who people are and their status in society that doesn't care how people feel.
I ended up with medical issues that took me out of my career and the work force in general for a while so I lost my financial independence, I still wouldn't call myself that, but I'm protected by my relationship and its standing with the law to a limited extent. Whether that's the best way to protect people is questionable, just as there have been many questions about the times the law treats people as individuals and the times the law treats people as a marriage or a household.
There are likely ways this could be improved, but how is a difficult question with so many factors in how the law works in social engineering with most consequences being unintended, but none of this is how people frame their own marriages. Making it an individualistic concept doesn't change that the reality is our marriages are viewed the same in the eyes of the law and someone by wider society no matter how we define it within our lives, how happy we are in it, how well we're treated in it, how much we benefit or are harmed by it, how financially independant we are -- it really doesn't matter much within the systems around us.