Remember how quickly all this can happen. SEALS train, practice, train, drill to be ready and reacting quickly becomes second nature. Even those of us who are trained in some self-defense skills may not react at high speed. We are not in combat preparedness mode. Protecting loved ones with their own bodies was all the brave could do.
At times this nutter's back was to people. Anyone try to rush him from behind? A veteran may done but not many civilians. Even the heroes of Flight 93 had time to evaluate and plan their courageous action.