A fascinating interview with Kirk Meyer, former Director of the Afghan Threat Finance Cell, suggests why.  Meyer reports:  The Taliban were collecting taxes on opium in the south. They were going to mirabs, who were the local officials who managed the water supplies in the villages. The mirabs knew which farmers were growing opium, and could estimate the size of their operations by the amount of water they used. The Taliban would have the mirabs calculate the amount of tax owed to the Taliban by individual opium farmers, and then also use the mirabs to collect the tax, which was paid in opium.

I went to a lot of meetings about crop substitution and eradication, but the problem with that approach is in the way the opium system works in Afghanistan. The opium farmers are given credit by opium brokers at the beginning of the growing season. This debt can be repaid only with opium. These opium brokers act like the company stores in the old coal-mining towns in the United States, where miners always had debt so they could never get out. Until they got their wages, they were always being paid in goods, and they could never leave because they owed rent on the house and money for groceries. Well, that was what would happen with the opium farmers. The opium brokers would loan the farmers money at the beginning of the season, and the only way the farmers were permitted to pay it back was in opium. Let’s say a farmer won the lottery or had some other financial windfall; he couldn’t go and give the opium broker money for his debt. The debt had to be paid in opium. So when the Karzai government eradicated opium or tried to substitute crops, it often worked against the individual farmers who owed debt in opium, and possibly made them into Taliban supporters.

I remember one farmer I interviewed who told me that when the government came and eradicated his crop, he couldn’t pay the opium broker, and so his father gave the farmer’s four-year-old daughter to the opium broker, who was some 72-year-old man, to try and settle the claim. Anyway, these young ATFC analysts came up with the idea that the military should focus on the mirabs and their relationship with the Taliban. We should wait until the mirabs gathered the opium owed to the Taliban for taxes, and at that point, conduct military and/or law enforcement operations, because then the farmers would be out of the equation. I believe that was the innovative thinking we should have been using to deal with Taliban funding through the drug trade.

You would have to monitor, either through legal wiretaps or other means, the phones of the mirabs, or recruit the mirabs as informants. By doing that, you should also be able to identify the Taliban members involved in the tax collection. This way, you could intercept the Taliban when they came to pick up the stockpiled opium from the mirabs.

Here is the December report of the US Senate Committee.  2014-12-23 Afghanistan Report Final