When there were still more than ten grand arrays left, the Nine Nether Nether Soldiers had only two or three dozen Buddha Kingdom Worlds remaining. That number was nowhere near enough to threaten Chi Xue and the others. In fact, if Chi Xue and the others deliberately tried, the Nine Nether Nether Soldiers might not be able to destroy any more arrays—certainly not all of them.
As long as even a few arrays remained, Chi Xue and the others wouldn't be forced to abandon them and circle the Demon God Forbidden Ground while dealing with the Nine Nether Nether Soldiers. They could use the arrays as stepping-stones to reach the Demon God Forbidden Ground as quickly as possible, then join Ling Tian and the Lord of the Universe's grand array.
However, to keep the Nine Nether Nether Soldiers attacking—or rather, to make them keep attacking for as long as possible—Chi Xue and the others didn't destroy every Buddha Kingdom World at once. Instead, they focused their attacks on the Buddha Kingdom Worlds, trying to capture as many as they could. This would undoubtedly let them capture more Nine Nether Nether Soldiers, especially since the soldiers could no longer destroy every array.
The tactic did indeed give the Nine Nether Nether Soldiers a false impression. At the very least, they didn't stop attacking at once. As long as they kept attacking, Chi Xue and the others had a chance to capture more of them.
This approach meant that a few more arrays would be destroyed, but as far as Chi Xue and the others were concerned, it was no problem as long as some arrays remained for them to "shelter" in at the end. After all, repairing the arrays was fairly easy for them, while capturing more Nine Nether Nether Soldiers