I remember an interview with a Russian military man just as it all started. Message - you wont succeed. Actually I don't think anyone ever has. The west was even supplying Bin Laden with kit when they were in. Shown on the TV posing. A commentator mentioned that this will be regretted as the bloke just hates the west, Russians too. He just doesn't like countries interfering. It's the sort of mindset it is all up against. Our way and anything else is out of the question. Sadam had been shown too as a defender of the west.
The reason usually mentioned is warlords, those have armies. This is probably why there is a concern about civil war. Last time the taliban controlled it the place seemed to be quiet. I read that they had more or less ended poppies by dying anyone caught doing it green - one of the Times papers.
2 reason rumours i noticed were a pipeline and lithium deposits. The obvious one is the Towers and terrorism. International politics may mean we will never know.
Seems to me that they should have left the place in a war footing. National subscription, the lot. Even that would be tricky when a member of a faction has decided to appear to be on one side or the other and then shoots the people around him.
Talks have been held with the Taliban which may be why they are making nice noises that don't tie in with what some of the population are saying. They may even have factions in their own ranks. Pretty likely I would have thought. I'd suspect they are staying out of the capitol really because there are currently 6,000 USA UK troops there and probably others as well to get their nationals out.