Drugs business only exist because authorities allow it, otherwise this thing would already be finished at this moment. Doesn't matter if there are cameras or any other system to track these criminals, if the person watching from the other side of the camera is a corrupt one (or his superior), nothing will happen. Drug trafficking movements a lot of money and involves several sectors of a society.
I agree, if the goverment would be strict about it it would be allmost everything gone... But there are people, who know that it's allways better to reduce "unwanted" population, especially now when we grow so much in numbers, plus, that means more money to the country(in a lot of ways) and some drugs for the politicans, to be even aware of himself on those booring conferences and meetings, and one extra plus is, crowd control, majority of society probobly have jobs to buy drugs for himself...