OP, I have the exact same thing, I believe.
I am in a very established career which makes me enough money to support my children alone if I need to. I have assets of my own, and so I am not financially dependent on marriage or need the legal protections in that way. I also look at marriage quite cynically because I know it doesn't work out very well for many women, there are lots of expectations and norms around it that I don't like. I didn't ever romanticise it, or sentimentalise it. However, I DO like the commitment side, that is important to me, far more now that we have children than before, so this is something that has changed in me, and I am allowed that change. If you are changing your mind, that is allowed, too.
We have had a lot of searching questions about it. For him, it is not so much that he doesn't want to marry me, it is his understanding of marriage and what he saw in his parent's marriage (it wasn't great). And he is not sure how to do it without emulating that. My parents have a marriage that is still going strong, though they have had the ups and downs one would expect from two people who are now mid-60s having married at 20.
We went through a very rough patch in our relationship since Covid, and we have been working at resetting things since. We know one another far better now, so that is good, but for me, I have wondered aloud to him and quietly to myself, whether we both would have behaved the way that we did if we were married. I don't know. On the other hand, I also think if we were married, we might very well have divorced, and once that was done - such a formalised rupture - we might not have reconciled.
The marriage issue is one I am going to broach with him again, and it will come up in our ongoing conversations and in therapy and I will explore widely what it means for me. If it at the end it is important enough to me and he won't budge I will rethink the relationship.
I say all of this as a woman who is 15 years older than we were when we met. Our history makes me think it might be more core a thing to us than I realised before.
Again, we are all allowed to change.