As a sitting target the Taliban was easy prey to the much better armed, better technologically equipped international coalition. Due primarily to an almost criminal ignorance of the forces allied in the region, the Administration of President GW Bush made a number of monumentally poor strategic decisions and then turned the most powerful military in the world away from its objective of "Dead or Alive" and pointed it toward an ill-defined mission of taking down a petty dictator in Iraq, not only diluting the hunt for bin Laden to the point of crippling it, but also fragmenting the international coalition.
The emaciated force left by the U.S. in Afghanistan, with some resources from traditional allies, stood alone in the abyss that is Afghanistan.
Afghanistan has been involved in conflicts for 4 times longer than the U.S. has been in existence. They have been arguing, as they did in the 1924 Khost Rebellion, "Islamic" and/or "un-Islamic" dictates and tenets almost since the beginning of recorded time.
Why does any of this matter?