The WOD is more than illegality. About half the DEA budget is for anti-drug advertising. The remainder is for drug interception at the borders and in other countries.
Marijuana has been illegal for 70 years. Our WOD has been in place less than half that time.
I simply acknowledged that factors other than illegality affected drug usage, either in a positive or negative direction. I never discarded illegality as the reason for the decline.
You should have, since once you acknowledge that factors other than illegality affected drug usage, your argument by correlation-thus-causality no longer has any foundation.