I’m guessing you don’t have kids and have not yet thought extensively about retirement.
Marriage is about responsibility sharing in a way that survives even the worst of breakups while keeping all parties responsible in a fair way.
I’m also suggesting you entertain a thought experiment where you swap genders in the relationship and also assume you have at least one child you love dearly and taking care of it takes about 100 times more time and effort than you currently think.
Now you might have an inkling why people get married.
Full disclosure: not married but have most if not all the responsibilities in writing with the mother of my children so she does not end up in poverty if we ever split after raising our kids with so much of her life love and health.
Try to see something from somebody else’s viewpoint. Basic empathy.
I’m not interested in changing your mind, OP asked for insight, this delivers it.