Almost every expert recommends better diet, exercise and sleep, so I’m not sure why you’re viewing the “go natural” statement as a necessarily anti-expert one.
It's "fuck off advice". They recommend it in full knowledge that almost nobody ever sticks to it, but it keeps the advice receiver busy and feeling responsible for their own problem.
Lifestyle change is hard and impractical even for most neurotypical people. With untreated ADHD, it's almost impossible.
Likely for the same reason why prescriptions are so popular. It is way easier to down a pill then to workout, changing your eating habits, or adjusting your lifestyle to allow for more sleep. Changing habits is hard, eating meds relatively easy... "So off we go, and man, if someone interferes with our narrative, we attack like the speedfreaks we have become..."