Why do people not get married but have a baby?

Okay, please don't be mad because this isn't a snarky question, I'm genuinely asking a question...

When people say they're not interested in marriage they say because of the commitment or that they don't want the legal trouble if they wanted to end it, but wouldn't you have all those same criteria if you have a bang together? I'm not talking unplanned pregnancies, I'm asking the unmarried women who are TTC. What other reason are there for not getting married?

Again, I'm not being judgmental, people have babies that aren't married all the time. Please be nice! Every time I ask a question trying to better understand a topic I get ripped to shreds. 😅 just tying to educate myself here...

UPDATE: thank you everyone for your comments, I learned a lot. Just to clarify though, I never meant to say that anyone "needed" to get married especially for religious reason. I asked the question because I know people who say they don't want to get married because of the commitment but also want to have kids. I never meant to imply people had to get married.