The big trio was having the most intense and powerful fight of all others. The Qi distortion waves created by them were able to influence even the other fights around them.
Not to mention that the Tang family 'senior' had to fight some annoying flies beside the duo at the 6th level of the Nascent Soul Realm.
While those flies didn't cause much damage to him, they were nonetheless really noisy, and unruly, and were driving him crazy.
Earlier he had already killed as many as were left, but he had also gotten a lot of injuries from the duo who were always ready to jump the gun and attack him once they found an opening.
While they weren't able to kill him, even if they landed their attacks, they still could cause him a lot of damage and were slowly eating up at his vitality, and strength.
But continuing like this was not a solution too, since if everything went on like this, he would be the one to die sooner or later.