Because politicians will largely enact policies which enable them to be re-elected. I don't know the specifics but I strongly suspect that coming out against t

Because politicians will largely enact policies which enable them to be re-elected. I don't know the specifics but I strongly suspect that coming out against the war on drugs will lose them more support than it would gain them. Support in terms of some mix of votes, finance, influence and connections. If this was un-true then some politician would have realised that standing for legalisation would win them an election and would have done so by now.