Earlier quoted context omitted.
I think you have it upside-down. It's tobacco and alcohol that have special treatment, not pot. My main guess for that special treatment is merely that tobacco and alcohol were global when we started taking care about global health issues, so we left them, but banned any newcomer
There are plenty of psychoactive substances on the shelves of any major supermarket and most of the stuff is completely unregulated. How is coffee different from tobacco? How is nutmeg or saffron different from drugs? How about artificial flavonoid—xanthine concoctions such as Red Bull?
In my country, 'energy drinks' cannot be sold to anyone under 20 (same as alcohol and tobacco) for exactly this reason.