I would guess this is because the Taliban are not signatories of the Geneva Convention, and as un-uniformed troops are not entitled to any of its protections.
While I was in the military, I asked why snipers use Match King hollow point bullets. It was explained to me that JAG ruled that military shooters cannot use a hollow point designed specifically to increase wounding but they can use a hollow point designed to increase accuracy. I was told that the hollow point manufacturing results in more uniform jacket thickness, better ballistic coefficient by moving bullet center to the rear and other factors that make them more accurate than FMJ rounds. This is why US military snipers have been allowed to use hollow point bullets for years. The better terminal ballistics are just a side benny of using the design which is supposed to be for accuracy. I do not know if this is true or not but it sounded good enough for me to believe it.