It's a lot older than that. The reason the drug war goes on is that there aren't enough votes to be gained by changing the policy. Further, as long as they can get money and power via appropriations to continue the war, there is little incentive to go after the excises and fees that would be associated with any legalized drug world. This is why even if a change were to occur, it would simply be a shift away from enforcement and incarceration towards treatment. Same concept:enact programs which justify bureacracy, jobs, money, and power. Simple.
Logical arguments have nothing to do with it. There simply aren't enough Americans who see legalization as in their best interest, and the advocates of legalization haven't found a way to make it appealing enough to politicos. Logical arguments or ROI analysis has absolutely nothing to do with the question in reality.