It's too early to speculate without a detailed report. On the surface it would seem that challenging an active shooter is a way to get shot. The person started the action probably discarding consequences. Some of these actions are really set ups for vengeance, making a statement and then suicide by cop.
I saw a re-inactment of some crime on the Discovery channel. Two bank robbers were challenged by two officers as they left a bank. From the show (who knows how accurate), one officer was shot and the others got away because of the officers repeatedly yelling to drop the gun while the bank robbers shot at them.
While you are talking, your attention and mental capacity is diverted from the action of observing the shooter, who thus gets a head start on shooting you. I've seen it in FOF.
Without real details,yet - it would seem to me that if you are facing an active shooter, challenging is not a priority.