As soon as the black dragon showed itself in the skies, the rest of the Canzers felt its oppressive aura try and repel them from coming forward.
If they were just by themselves, they would have immediately turned around and left the place. Who cared if they were going to inherit a kingdom if they were going to die for it?
However, there were thousands upon thousands of other Specialist-level Canzers here with them. They weren't alone. This gave them the hope that maybe, the black dragon wouldn't be able to kill all of them. And somehow, one of them would be able to penetrate their defenses and kill the humans.
They were hoping that others would get killed, and they would survive long enough to inherit the Kingdom. That was what they were all thinking when they faced the black dragon.
They rallied under the assumption that the black dragon couldn't kill all of them.