I have a view that people have a personal responsibility to maximise the resources they can for their kids, which tends towards having children later.
As I said, someone is always picking up the slack for people who do not - whether that is through help from friends and family or the state.
I worked to have a nice life for me because I actually like myself, and I wouldn't want to have a kid in a situation where they would have a worse upbringing than I did. I also wanted to travel, work on my mental health, take career risks, and find the right partner because those would be good things for me as a person which in turn would be better for my child. I earn good money and have had enough experiences where I would not feel trapped by my circumstances - and hopefully can raise a fully-rounded human being.
You don't need all of that, of course, but I see my peer group that had children before earning decent money, or finding the right partner, and their lives just look shit. Fighting all the time, stuck with each other, living in too cramped flats in rougher schemes, being skint all the time, never going on holiday (or even a date!). And they are so bloody boring - because their kids are the only things they have. And I'm sure they would say that it's all worth it and "they made it work".
It's not the type of life I would want for myself or a child. I'd rather have the best life I can and then have kids as a much wanted and planned addition, rather than because they just happened.