Because when they use the Tathagata Buddha Scripture Technique, they need to calm their minds, so their attention isn't concentrated. Moreover, they would never have imagined that someone with the Great Perfection Limit strength of the Celestial Dao Seven Stars would have such powerful attack capabilities, beyond their imagination.
Actually, this is thanks to Chen Tianlong's Dragon Slayer Sword enhancement and the subtleties of the Nine Yang Celestial Dragon Technique. Although Ten Thousand Swords Return to the Root is a third-level swordsmanship, it tends to focus on concentrated attacks with a relatively small range. In contrast, Sword Roar of Nine Heavens has a large attack range, and its total attack power is somewhat greater than Ten Thousand Swords Return to the Root, but it's mostly used for long-distance, wide-area attacks.
