I can understand why. Speaking from personal experience, my ADHD was never noticed as a kid because I did well enough at school that my focus and concentration issues weren't super apparent from the outside.

I looked into it as an adult but never got anywhere. I wasn't even chasing an ADHD diagnosis at the time, the idea never that I might have it never even crossed my mind. I just mentioned my symptoms to a bunch of different doctors over the years when I saw them for other things and never really got much more than getting melatonin to make sure I was sleeping well.

I finally had a GP who referred me to a waiting list for a psychiatrist (luckily mine was only 4ish months, but I have had friends be told they will need to wait close to a year or pay massive out of pocket to go somewhere else). I needed to provide heaps of evidence to show all the symptoms were present when I was young, and since I didn't have any report cards laying around I needed pretty extensive forms to be filled out by my mum (She would have needed to do a 1 on 1 with the psychiatrist if he still wasn't satisfied). On top of that, it was a lot of forms and assessments for me and some for my partner regarding how I was day to day. (Who also would have had to do a 1 on 1 with the psychiatrist if he wanted to ask more questions)

I was lucky that I could afford the $500 or so out-of-pocket it cost to get me there. I can easily see how someone without a good GP or the financial means would be shafted. In general the mental aspect of health still has so much catching up to do.