They're not the only ones who benefit from the drug war. It's a tool in order to allow for mass incarceration of "undesirable people". The book "The New Jim Crow" by Michelle Alexander really spoke to me as a resident of Philadelphia. I knew full well that if a cop found 1/4oz of weed or less on me, they wouldn't do anything...but if I was black, I'd be put in jail. Now that marijuana has been "decriminalized" (I call it "equalizing" the law because it's now fair for all people) in Philadelphia, that's not as much of a problem in my city...but I'm pretty sure statewide it's still a big problem. Essentially, I think the drug war is a big, lame excuse for putting people in jail.
This is actually a very interesting aspect of the dangerous results of having lots of laws and bans. It is like companies which makes long lists of things which can get you fired. List which are such that everybody has done a fireable offense. This allows companies to fire people at their own discretion because they will always have something on you.
Likewise the corruption laws in developing countries seem to largely be about getting rid of political opponents. Everybody is basically guilty of corruption, but only those who are on the wrong side politically actually get prosecuted. Look at Russia, if you cross Putin they can charge you with corruption right away because they no almost everybody has done it.
In this regard laws which masquerade as fighting undesirable things in society really becomes a tool of oppression.
https://en.wikipedia.org/wiki/The_New_Jim_Crow