Well it isn't. The more the police win the war on drugs, the more potent the drugs have to be made. Because they are easier to smuggle in smaller quantities. That is why there is such a big problem in North America. They started winning the war on heroin. So the drug business opted for fentanyl. In Europe, the more bulky and safe Afghan heroin can still get in over land. So way less people in Europe die from fent overdoses.