There were literally hundreds, perhaps thousands of very convenient coincidences on 9/11, all having the effect of helping to facilitate the attacks. This is just one of them. There were 12 war games going on on 9/11 where a large portion of the air defense system for the Northeastern US was sent towards Alaska, rendering it impotent to defend the Northeastern US. 4 of these were deliberately rescheduled for 9/11/01.
Michael Ruppert wrote of the various training exercises conducted under the cover of "Vigilant Guardian" on that day, in his book "Crossing the Rubicon". The war games set the tone for deception that morning.
The spoofed radar with fake targets lasted until afternoon according to Ruppert. That contributed mightily to the confusion of the ATC system, as planned.
