Because the Jet was on paper tight on performance (the Mission Computer is always a little pessimistic) and the runway is only 3800ft long, so for the USAF to do it would have required really careful planning (it arrived direct from Iraq) and an immediate refuel on departure...that and the fact it arrived at BZZ totally unannounced!
BBC NEWS | England | US sends aircraft gift
for BBC link....Spoons on Speed!