Local gangs are partially funded by cartels with international drug empires funneling cash from places like the United States.

Making drugs illegal doesn't prevent people from using them, the demand is still there and someone will fill it. It just inflates the prices because of the layers and dangers involved with importing the drugs, there is no tax revenue, and the money eventually leaves the country instead of being recirculated like a normal economy.

And that doesn't even get into the societal impacts. Or the underlying mental/psychological reasons people turn to the drugs in the first place that aren't being addressed by society. But it does mean a nice constant stream of "criminals" into the penal system that can legally be used as slave labor.