Resource scarcity.
Because more resources are hidden within the immortals.
Slaying a lower-ranked Daluo might be enough to forge ten thousand robes like this purple and azure Dao robe.
Slaying Wang Wu could also produce a thousand such purple and azure Dao robes.
This is the biggest difference with the Dao Fire Realm; they genuinely cultivate the weight of the unique Dao in their process of cultivating the unique Dao.
It's equivalent, theoretically, to all cultivators in the unique Dao system—Earth Immortals, Taiyi, Half-step Daluo, Daluo—being shareholders of the unique Dao.
While in the Dao Fire Realm, all equity is with the world's ecology, all living beings—even those becoming protagonist beings—are just gilt-edged laborers.
Of course, this is just a metaphor; the Demon Race Supreme Celestial Emperor certainly wouldn't consider himself lower than an ordinary Taiyi on this side.
