Law enforcement dollars is much bigger than the DEA. Think of all the local and regional task forces, and especially the prisons. That's a lot of money, salaries, services, profit.

So there's a source of campaign contributions and other lobbying efforts, or bribery.

And then there's the purely political side. Very few politicians will come out in favor of legalization or decriminalization. Not because they care one way or another. They just don't want to hand a brick to their opponent, which will be used. "Candidate Sluggo is soft on drugs, soft on crime!"