I think most women have a very good understanding of timelines for the average woman.
I think that issue is that most women assume that they won't have any fertility issues, especially if they have had no warning signs that there may be a issue with their fertility/reproduction system.
I can't have children. Started seeking medical help at 13/14 but it took until 27 to get a diagnosis. In my case, it was pretty obvious something was wrong but a lot of people don't have any obvious warning signs.
In our teens, the messaging is: it only takes one time, be extremely careful with contraception, it is hammered hone so often etc. so it's unstandable a lot of people think it will just happen when they start trying.
While it's easy for a lot of women to get pregnant easily, there still has to be a lot of things working together to make it happen timing, egg/sperm quality, amh, thickness of lining, lenght of folicals etc. Any one of these can have a major impact.
The stats re ideal amh, success rates re ivf, iui, donor eggs, egg freezing etc aren't commonly known & most people don't become aware of them until they know they need assistance.
People assume they are going to be the norm & generally only know the standard stats.
I have a very high amh & even once enquired about donating eggs. I can't use them so though it would be good for someone else to if they wanted. I was told they were too old to be donor eggs - I was early 30s at the time. Given that's when most people start their families, it never crossed my mind that they would be too old. Naive perhaps but it was just not something I ever considered.
I think it would be great if a full female health check was encouraged in late teens/early 20s so that people who may struggle to have children realise their position earlier & can may be able to do something about it.
Typically, 20% of women still struggle to have children. It makes sense that most people assume they are in the other 80%.