At this point, even if Daoist Priest Qing Yun was unwilling, there was no other way. After this battle, it had become clear to everyone that everyone was just enjoying themselves after a whole night of waiting.
My guess is that the last monster was born from the Heavenly Dao. Its goal was clear, and that was to stop Yao Yao from reviving.
Once Yao Yao failed, it would immediately leave