Supreme Divine Power, learned by many, but to truly comprehend it to perfection is no easy feat.
Don't think that just because Yang Ji could perfect a Supreme Divine Power in just a few hundred years that everyone can do the same; that's because he had the super comprehension aided by the Golden Finger, which others find nearly impossible to achieve.
Ordinary cultivators, let alone perfecting a Supreme Divine Power, might not even be able to understand a Great Divine Power.
Even among Red Dust Immortals there are vast disparities; in over five thousand years, Yang Ji had fully mastered a top Immortal Technique of great Immortal Technique volume, yet the three old ancestors of the Immortal Cauldron and those Star Brigand Kings were still stuck at the introductory phase, with Jing Po unable to even step through the door—the gap between them was just too vast.