There are plenty of interested parties that want the status quo - prison's would be emptied if they stopped arresting for marijuana as there are thousands in prison and some for minor infractions. The local police would have a revenue stream interrupted as they get funds for drug busts and arrests as well as federal forfeiture of assets. Politicians would lose a pinata to bang every elections as being tough on crime. Not counting the money that changes hands between police, politicians, and drug dealers.