I think that you're right and that this is one of the predominant reasons for declining child births.
I think that if I were a woman that I would personally choose career or personal life first before having children, all other things in my life held equal. I have a lot invested in those things, they're here and tangible, and they bring me joy.
Media says that it's the economy, but I've never once believed that to be the leading factor. People had babies when they didn't have fresh food, running water, or even homes. Certainly far worse lives than we have today.
Peter Zeihan, whose YouTube prognostications seem iffy, likes to call children "expensive furniture". They were useful labor on the farm a hundred years ago, but in small apartments they can be a real nuisance.
Modern parenting is wild - there are too many rules and regulations and things just have to be just perfect to have a kid. Our great grandparents just had them all over the place and would let them roam around in the wilderness. Today we have to coddle and bubble wrap, sign them up for classes, take them places. Just thinking about it seems stressful.
At the same time, we've got these little dopamine cubes in our pockets that are taking our time away from socializing and dating and meeting people. It takes time and deliberation to find someone to settle down and commit to raising "expensive furniture" with for the next twenty years. You can just keep scrolling your feed and filling life with experiences.
Perhaps instead it's that the modern life creates the perception that something different or exciting could be just around the corner - like a kind of hedonistic treadmill, or wishful longing. Our ancestors just accepted their fate and lived their short lives. We have too many things taking our time and attention, and everything has to be "perfect" before we commit.
Not making any value judgments here, just stating observations.