Why is opium production reaching record levels in Afgahnistan while the US and now Nato are entrenched there?

I find it interesting that the Opium crop (the plant that produces heroin) has reached record levels during U.S. and NATO occupation. Why is that? The profits produced by this crop are obviously providing financial aid to the Taliban and also terrorist networks. The Opium produced in Afgahnistan is responsible for 90% of the Heroin sold throughout the world. Wouldn't it be possible, now that U.S. and NATO forces are there to destroy this crop? Couldn't we perhaps carpet bomb the fields? Why is that the TALIBAN was able to reduce Opium production in Afgahnistan down to almost nothing in 2000 and now the countries that supposedly are waging a "war on drugs" are allowing production of this drug to rise back to record levels. Is it possible that the long held conspiracy that the U.S. actually wants drugs in the U.S. is true? That the drugs help provide an income for the U.S. government and also hold down the lower cles? Not a conspiracy theorist, just curious. Your thoughts?