Afghanistan was never about terrorism. I think it more likely that it was about opium (one more in a series of wars for it) and making sure that the supply didn't vanish, as the Taliban were banning it. But when they were kicked out, they resorted to selling it in order to fund themselves. Now they're used to it, I imagine by telling themselves that the corrupt western infidels are welcome to it. The poppy milk will keep flowing and everyone will be happy. Except, of course, for the Afghan people.

As a side note, with the country "pacified" under the Taliban interested parties can negotiate lucrative mining deals for the considerable mineral wealth of Afghanistan. Cheap labour, non-existent pollution regulations, no questions asked, perfect.