I appreciate you sharing your experience. And yes, I’m well aware that knives (and batons even), can beat a gun in short ranges. The famous Filipino Eskrima fighters of the early 1900s (the culture my parents came from) taught that lesson. And legend holds that pistols like the M1911 were specifically designed for those close-quarters combat situations (too many US soldiers dying to the Filipino eskrima stick fighters that US paid R&D to figure out a solution back then).
But the hallway of a school can stretch many dozens of meters, far longer than the distance you can close with a knife, and even stretching the effective firing range of a pistol and knife.
And given even the presence of a door: the knowledge that the AR15 on the other side could likely penetrate the door makes breaching operations difficult. And the presence of hostages / kids in the classroom prevents many weapons / breaching techniques from being used.