Categories Z00-Z99 are provided for occasions when circumstances other than a disease, injury or external cause classifiable to categories A00-Y89 are recorded as "diagnoses" or "problems".
Organizations running programs for such children had incentives to diagnose problem children as having the particular problem for which government money was available.
The main issue is that the amount of diagnostic images out there in the wild increases at a staggering pace, and it makes it more and more infeasible for doctors to look at.