Given this situation, since it was their defense that kept Zhou Tian from breaking through all this time, those living beings certainly didn't want to provide Zhou Tian with an opportunity to make a breakthrough at this moment. So, under these circumstances, when they saw that Zhou Tian might not actually be in the underground cave, they naturally had to reinforce the defense line of the outside world.
Everything turned out just as Zhou Tian had anticipated. Although at the beginning, those living beings were indeed thinking of wiping out Zhou Tian, their enemy, in one fell swoop, once they realized that what they were attacking might merely be Zhou Tian's "doppelgängers," they certainly confirmed that they would have to withdraw some of their military power from the frontline.