"...illegalization doesn't meet its purpose (making drugs difficult to get)..."

This is a common assumption about the purpose of drug prohibition, but historically things are more complicated. Racism played a much bigger role in drug prohibition and the war on drugs than genuine concerns about public health. The basic concept is that some non-white group is corrupting white youth/white women with drugs; therefore, to protect white people, the police are empowered to imprison/kill those scary drug peddlers. On some level it was about making drugs harder to get, but the assumption was that white people have no interest in drugs until some non-white person pushes it on them. The assumption was always that the impact of drug prohibition would be mostly concentrated on non-white populations.