I've always wanted children, loved children, loved the role of caring for / playing with children. I have 3 and I think if I had the resources I'd have 4. I also work with children as my career.
I think because I've always wanted children / to care for children so much, that's always made it kind of obvious to me, that if you don't have that motivation to at least some degree, then of course you wouldn't choose to have children. Because yes, very often it is enormously consuming and stressful and there is little left for much else (at least whilst they are very small).
I find it strange in a way how we even phrase this decision as "having" or "not having" children, when really I think it's about being or not being a parent. I think the question "do you want to perform the role of a parent?" is a much better way of putting it. Because it's more like taking on a lifelong vocation than it is like acquiring a thing. We don't really have our children, they don't belong to us. We fulfil a role toward them.
I think another thing to remember about this discussion is that whilst many people don't become parents, almost everyone is the child of parents. Our parents and grandparents are probably our most influential connection to older generations and most of us are likely to get a pro-natal impression from them because they chose to become parents themselves.
Much like kids of firefighters may feel more encouraged to become firefighters than screenplay writers, as a general trend. Parents tend to, sometimes on purpose, but often inadvertently and unconsciously, lay down a path for children to follow in their footsteps.