"Children seemed the much bigger commitment (to me at least, I know others will disagree)"
I agree, and I think most women do. Because for a woman having a baby is an enormous commitment in that it usually makes them dependent (at least temporarily) to the father.
There are (rare) men who don't "believe" in marriage.
But far more common are men who very much believe in marriage, but don't want to get married to the woman they are with.
Some of these men are willing to offer a baby to keep their domestic service and regular sex arrangement going, and don't see it as that much of a commitment.
They see a baby as being the woman's business, and don't intend for it to change their life at all (and we all know that there are men whose comfortable lives carry on as before when a baby comes).
The big change it will make is that it's the best way to get the silly bitch to STFU about marriage. Many don't even realise in advance how compliant a woman with a baby will become, and how much advantage can be taken of maternity leave to craft yourself a little housewife.
Men are socialised to take what they want. A man delaying, being vague, sulking, refusing to discuss and offering things to keep you there for the moment, does not want to marry you.
If you go ahead and have a baby with him, you're likely to end up raising the baby alone. At first because of his lack of involvement, and ultimately when he leaves you to marry someone else.