Maybe that's the case in some cases but I'm not sure why people are determined to ignore the fact that the economic landscape in the UK means it is extremely difficult to manage.
Just looking at housing alone; I got pregnant young in 2015 and even then couldn't afford to rent, nor was I competitive as prospective tenant to professionals who could afford to rent a family sized property for themselves. It took about 18 months all in but eventually I got a home. It's not council but also not private so I have secure tenure.
These days, it's becoming increasingly difficult to get any sort of stable housing at an affordable cost, and of course when you are considering having a child, that's a huge factor.
It is extremely obvious that plenty of adults who would happily slipped into parenthood as a natural result of having a happy relationship and a settled home, are no longer living in situations where that can happen.
It's really not rocket science and while it's great that people are being discerning and choosing not to have kids, it is definitely not the only nor likely the most common reason people are not having kids.