Because history proves winning the war is easier than maintaining the victory. Britain, the Soviet Union and the US easily took control of Afghanistan but they could not manage the victory and were eventually forced to leave in a disgraceful manner.
That's the truth behind the whole thing, maintaining the victory is always where the problem lies. Being open about the press conferences is a mare declaration of the actual to come as, I don't believe any such good governance would come off a Taliban rule. It is a rule instilled by fear and when a people, a citizenry is held together by fear or force, your sure to experience revolt in time and this is what would become of the Taliban rule in time.
You can imagine a sole idea of a sole religion conjugate about this which is a direct hindrance to freedom and freewill. It doesn't tell so well for the well being of everyone, foreigners inclusive.