He could still remember his first fight in the upper realm. It was against Black Chain, and the Dao Lord of the Four Directions Sect had nearly enslaved him.
If he had succeeded in crippling Black Chain at the beginning of the timeline with his trap, he wouldn't have anything to worry about. But Black Chain was at his peak in this timeline and could even grow stronger, making him more dangerous than ever. So he decided not to take any chances.
Then there was Heavenly Eye. Even if he blocked the four worlds from accepting the Domains of Dao Lords, he couldn't stop her from establishing her Domains there. Therefore, as long as the four worlds remained, Heavenly Eye would grow more powerful.
As for what she could do with that power, the first thing that came to mind was her slipping past White Loki and joining the Olympic Sect. She had done it before, so she could do it again.
