Hip-shot hypothesis: The productivity literature audience is overwhelmingly intelligent people with untreated ADD & ADHD.
I disagree, it's possible to find hacks to change your own behavior and even how your body works, these hacks can then turn into habits and long-lasting behavior.
I'd add anxiety (GAD or things like that) to the list.
Also, all the coping mechanisms you've built up over the years can easily mask the problem. We used to ask people "Can you dress yourself?" to assess if they have manual dexterity issues. The problem is, almost everyone says "Yes". The people with the dexterity issues simply wear loose clothing and never buy anything with buttons. They probably haven't even thought about it for years, it's just their normal.
Mental issues can be similar. I've you've got through to adulthood you likely have a huge range of tricks, some of which you don't even think about anymore, to help get you through the day.
I see your point.
Then again, one of the problems for some of those are that they start way too many thing.