I believe a significant factor is we, including myself, we sold the dream by celebrities that everyone can have a baby pretty much close to 40. If you just keep yourself healthy.
So I didn’t consider having a baby until age 33/34, cracked on with my career for 10 years, struggled with conception which takes two or three years of whatever method.Then you are aged 37 with a newborn, and the idea in a year or two of going through all of the IVF again almost age 40 is horrendous, so you just stick at one child. I know loads of friends who did that, we adopted, but we didn’t get round to it till I was age 34.
When we were young we were taught that if you had sex there was a high risk of getting pregnant and you must immediately run to get the pill, but it’s actually so much more complicated, that the stars must have to align sometimes. So we all just ignored it and thought we could have sex twice and get pregnant. It’s only now that me and my friends all know that we left it really late, most of us have a child by IVF, or adoption, but it was so much harder and we all left it so much later than we probably should.
My friendship group was about 10 of us, and six of us have one child, one has two kids, and the rest don’t have any. Pretty much all the same stories above.