The Eternal Divine Kingdom could only preserve the consciousness of the Heroic Spirits, not their souls. In the last moments of battle, the souls of most warriors were shattered to pieces; only a sliver of the True Spirit remained, which Shen Hao preserved under the influence of the Eternal Divine Kingdom and the Emperor.
This is why, at first, summoning the Heroic Spirits for battle required the consumption of Shen Hao's power.
Because, in the strictest sense, the Heroic Spirits only retained their consciousness and experience, not their Extraordinary Level.
Even their knowledge was difficult to advance.
After all, the thinking of the Heroic Spirits relied on the power of Shen Hao; they still had memories, but continuous learning and contemplation required the continuous consumption of Shen Hao's power.
In such circumstances, becoming a Heroic Spirit meant life was devoid of pursuits and hope.
Therefore, most of the time, most of the Heroic Spirits were in slumber.