It’s thought one of the main reasons the CIA is involved in drug trafficking is to raise funds for operations without having to get congressional approval or other oversight.
Even more: US invaded Afghanistan immediately after Taliban managed to destroy almost all heroin production. I don't think it's a coincidence.
There're reports of people who visited Afghanistan after US invasion and they reported that it feels like US army guards poppy fields. It would be very easy for US to destroy them, but they behave like they didn't care.
I think that's was the main reason for Afghanistan incursion: to kill two birds with one stone. Earn lots of money and flood Russia (which US hates) with drugs.