Watch the movie "Charlie Wilson's War" and you would find out how arrogantly and irresponsibly the US left afghanistan in a mess back then leaving all the burden and mess for Pakistan to deal with. A very selfish move by US.
US interest in Afghanistan was to remove Soviet influence ...... once that was done they moved on ...... what is wrong with that. They removed an external force / country and the it was upto the afghans to sort out their differences!!!!
I am sure if US had stayed a day more after the Soviet withdrawl everyone would have started calling them an "occupying force" . What happened in Afghanistan after Soviet withdrawl was an internal Afghanistan mess and they should have sorted it out !!! Everyone likes to have a scapegoat and US is the favourite one in this part of the world (not that they have not created their share of mess around the world).