Because you will never stop the demand for illegal drugs.If it is legalised,the quality can be assured, it can be taxed and some of that money can be used to support addicts,it will cripple the income of criminal gangs.The authorities can not and never will be able to stop the illegal trade of drugs, and the profits made by criminal gangs unless it is legalised. Sadly it is a war the authorities can't win and only ignorance and stubbornness has prevented them from taking radical measures years ago.