Comment by falk

Because the U.S. government secretly loves to profit off of both the direct selling/transportation/etc of drugs and the prison industrial complex.

I recommend you read the following for more details and proof:

The Politics of Heroin: CIA Complicity in the Global Drug Trade

http://www.amazon.com/The-Politics-Heroin-Complicity-Global/...

http://en.wikipedia.org/wiki/The_Politics_of_Heroin_in_South...

Acid Dreams: The Complete Social History of LSD: The CIA, the Sixties, and Beyond

http://www.amazon.com/Acid-Dreams-Complete-History-Sixties/d...

The New Jim Crow: Mass Incarceration in the Age of Colorblindness

http://www.amazon.com/books/dp/1595586431