TTC before marriage?

I just want to start by saying I’m not trying to be rude or attack anyone. Im genuinely curious about the answer. I realize not everyone is into traditional institutions like marriage and everyone has their own path in life.

I am in no way saying that I think it’s wrong to do this or that. You do you!

My question is...I see people post that they’re ttc with their boyfriend. Why are you willing to have a baby but not willing to get married? Is it that you just don’t want to pay for a wedding? Or you don’t want to deal with joint taxes? Or you just don’t care to be married?

Again I have no issue with it, I definitely don’t believe you have to be married in order to share a life together or be good parents. I’m just wondering if there’s a reason behind it.