From the point of policy and scientific fidelity to the legal standard, the switch would be a no brainer, but the DEA has repeatedly refused to acknowledge this reality in the past. Wikipedia summarizes these efforts. In short:
The Controlled Substances Act provides a process for rescheduling controlled substances by petitioning the Drug Enforcement Administration. The first petition under this process was filed in 1972 to allow cannabis to be legally prescribed by physicians. The petition was ultimately denied after 22 years of court challenges, although a pill form of cannabis' psychoactive ingredient, THC, was rescheduled in 1985 to allow prescription under schedule II. In 1999 it was again rescheduled to allow prescription under schedule III. A second petition, based on claims related to clinical studies, was denied in 2001. The most recent rescheduling petition was filed by medical cannabis advocates in 2002 and, as of May 2010, was being reviewed by the Barack Obama administration. Currently 16 states and Washington D.C. have legalized the use of medical marijuana, and hemp products are sold widely in the U.S. today.