Because drug treatment programs are, in the main, feel-good endeavors.
There are two federal drug treatment prisons. The BEST results they've ever obtained - graduates being drug-free after one year - is a piddly six percent.
Conversely, a significant percentage of Viet Nam veterans returned from Asia addicted to Heroin. Virtually all kicked the habit on their own.
Druggies are druggies.
Turkey has some pretty good drug laws...