Just look at the amount of heroin produced in Afghanistan before US invasion and after (hint: it's increased by orders of magnitude).
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.