Those countries that had were pressured by the US to stop. These countries (Morocco, Turkey, Iran ("Persia"), Iraq, Afghanistan) had large addict populations but none of the crime and antisocial behavior we see in the US and UK that's associated with illegal junk and the methadone clinic scam. Where there is grinding poverty, hopelessness, and disease, there is a corresponding market for opiates, but not everyone enjoys them, and to paraphrase Ron Paul, no normal person will suddenly decide to take on a junk habit just because he can without prosecution.

The Swiss had the right idea but did not go far enough, did not prosecute public nuisance junkies.

England's maintenance scheme didn't work because it restricted legal sales and possession to "established addicts" and naturally they diverted their legal supplies, selling to their fellow junkies and to casual users for profit.

If anyone 21+ could buy their heroin over the counter there would be no incentive to sell to others, unless the state ill-advisedly jacked up the price per dose with a tax or pharma companies inflated their prices.

Opiates are extraordinarily inexpensive, with a month's supply costing less than 30 USD retail.