The form of eternal life mentioned by the Wheel King made everyone unaccustomed. Giving up one's physical body, would that still be a human? Maybe that's what they call an immortal in legend. However, they weren't too taken with the idea.
After all, they had seen the terrible state of the corpses in the Nine-Layered Sword Pavilion. They guessed those bodies had deciphered the secrets within the White Jade Stone Tablet, thus enabling them to live for nearly ten thousand years. Even if their bodies rotted, their Primordial Spirit remained intact.
However, the Secret Technique the Wheel King mentioned wasn't complete. The contents of the eight White Jade Stone Tablets were just a part of it. He probably only managed to cultivate half of it.
Even though the Primordial Spirit could leave the body, it had to be attached to the White Jade Stone Tablet. Perhaps the complete version of this cultivation technique was much more powerful than what they had learned.