Corporate lobbyists and market regulation. Politicians would lose a lot of money personally if prohibition was lifted, so they won't do it.
The laws are there to fill jails, so we need more laywers, and judges, so we need more colleges to grow more laywers and judges, then we build more jails...whoever said perpetual motion is not possible! http://dunwalke.com/resources/organizations.htm
It's simple marijuana is too good. It works for too many things for it to be allowed. It has the potential to replace cotton, hemp is a better fiber then cotton, and it is MUCH less harmful to the earth grow it on a large level. If enough hemp was growing we could actually start to reverse some of the effects of global warming that are brought on by excess Co2 from livestock gas. Then there is the pharmaceutical industry. Medical Mariejeanne treats many conditions, but they can not make any money off it, because they are unable to patent the chemical formula for cannibas. Therefor there is no profit for them, and they lobby to keep it illegal. So the only alterantive many have is their drugs, which many people who have no interest in getting stoned will say are inferior to marijuana. They are simply dealers who mussle out the competition. The same thing with alcohol, they pay big dollars to air those above the influence anti-drug ads. They work for decades to create a language that separates them from other drugs. The term is always "drugs AND alcohol", as if somehow they are not like those "other drugs". I am not advocating alcohol be illegal, but I think we all know that when we are in public and someone is being violent, or annoying, are they generally drunk, or stoned? But they have been working this lie for so long, people ignore the fact that the "legal" drugs like alcohol end up creating more problems then the illegal ones. Alcohol and persecution drugs kill far more people in a year then all illegal drugs combined. Never mind all the domestic abuse that is a result of someone having too many drinks. Stoners tend not to be aggressive when high.