Because the "official" line for the umbrella of SEN is 20%.
And I still don't know where your "official" 1% comes from because I haven't seen a source for it anywhere. I used autism because it's the only thing I have ever seen quoted at 1% and as others have said, I believe this is outdated.
I am not trying to downplay anything, honestly. I almost feel the opposite from your posts, like you are trying to play the whole thing up for some kind of shock/horror value - I assume because you are concerned that this is a big problem and you want people to see that it is a real and concerning issue. I just think that inflating figures and presenting them in a misleading way is unhelpful.
I am actually very interested in the link between ADHD, ASD and trauma because I believe there is something interesting to be uncovered there, probably related to the functioning of the nervous system. In management of my own/my DC's ADHD I've found reading around the nervous system regulation incredibly helpful and I think more research would be good here.
I am defensive however of positions that ADHD/ASD is "often" misdiagnosed trauma because this is a narrative pushed by certain parts of the alternative health industry and IMO, it's a distraction. I don't think it overly matters what exact diagnosis somebody has if it means that they can access support which may help them. But the supports for ADHD/Autism are more comprehensive than support for trauma so I'd prefer to err on the side of overdiagnosis in that case especially as I believe historically these conditions have been underdiagnosed and likely still are. I can see that diagnoses of these conditions are rising, and like another poster, I think this is a good thing overall, and I think they will plateau.
I do think the current state of the health services is a problem because I agree that it seems they are overloaded and possibly poorly designed in terms of when you seek an assessment, if I understand correctly, children/adults are put in for assessment of a specific condition rather than some kind of general examination which might uncover more of a clear picture. I remember in the 90s/00s when I was at school, I had a lot of friends who were diagnosed/identified as having dyslexia, but now that we are all adults, a significant amount of them have found that actually, they are also ADHD/ASD but this wasn't picked up at the time, and the difficulties they have with things like sequencing, or understanding sarcasm, or organisation, which were put down to their dyslexia, could have been equally or even better explained by their other ND condition, which was missed. It's quite possible we are seeing something similar to this now, where ADHD/ASD are the first thing people jump to and if you get put through that assessment first, then that's the answer you'll get. But I don't think that questioning the diagnoses themselves is the answer to this, I think that is a risky approach which can cause harm.