Well yeah...
I know a bunch of young people 27-33 ish who are really quite immature in many ways, even though they have a University degree, and a home, and have travelled extensively, and have a successful career. Despite being smart and clever, they are in no way, even close to being ready to have a baby.
30+ years ago, most people I know were married at mid 20s or younger, and had their first baby by 30 - even the 'career' people with good jobs and a University degree. Most have coped fine and raised good kids.
Millennials seem to be more immature at say, 30, than the generation before them, and many of them seem barely ready for the responsibility of a baby even at 32-33. And some are just not having children, because they don't fit in with their active, travelling, career-driven, need-my-me-time lifestyle, where they're bored easily and always looking for the next exciting thing in their life. They also don't like the idea of the commitment of a child.
Some young people I know (around late 20s/early 30s,) are lovely kind intelligent hard working people, but no way should they have children. Maybe in 5-6 years. Maybe. Possibly never. They just won't be able to cope with them IMO. I don't mean ALL millennials of course, but some (and Gen Z too.) In addition, I know some millennials who have had a baby (or two) and are genuinely struggling with being a parent. It's hard work, and it's derailed their life.
Some of them are having a really rough time with the culture shock of having a baby/babies, losing their freedom, and not being in control of their life anymore. They had it good/all their way for many years with growing up in a softer, hand-wringing, no child ever loses society, and this baby controlling them is a hard pill to swallow.
As I said, the world could do with a drop in the population of humans. That's a hill I will die on. I'm not changing my mind. Even if anyone does say 'oh but we neeeeeed lots of new people on the earth to support the old.' Rubbish. Most young people don't do that, and where do we draw the line? Have babies purely so we're not alone as an old person? Rubbish reason to keep over-populating the planet!
Also, as has been said, there is SO much more these days for women to do with their lives, and they no longer have to be this baby making handmaid that society expected some years ago. As someone said, women ultimately DO end up doing fucking everything when they choose to have a child and become a housewife/mother: all the childcare and housework and grunt work and life admin, along with a hit on their career. And many women don't want this life now.
Of course this isn't the case for ALL young women, but some yes. So some will have babies. Need to keep the human race going, but a drop in population will do the planet good!