Because they're incredibly fast, exceeding 40 meters per second. You can't fire a shotgun at 80 meters. A typical shotgun's effective range is only 40 meters, and once it's within range, you only have one second to fire.
Furthermore, drones are generally difficult to detect at 400 meters unless you're using a synthetic detection system. By the time you spot them, it's too late.
Furthermore, drones are generally difficult to detect at 400 meters unless you're using a synthetic detection system. By the time you spot them, it's too late.