Reasons

"That's not the only problem. You should remember that there are a lot more cultivators who've entered the natural formation back then. Unless the Lakure Race members killed all of them, we shouldn't be the only ones present testing their defenses at the moment."

Roan was right. The sects and the Jialin Royal Family entered the formation before. There were even the Guntao Country's forces that Rean's group didn't know. Could it be that none of them were testing the defenses in the valley or attacking the crystals?