Thus, he dared not let other Evil Spirits devour him, fearing that doing so might threaten his own position.
But Feng Yin saw through it without pointing it out, instead acknowledging the other's strength: he had realized that this Abyssal Master, due to some kind of shackles, was unable to devour the peace cultivators, but could devour Evil Spirits, turning them into his own power.
In that case, Feng Yin preferred to use its ability to let him eliminate the Evil Spirits himself.
Another reason was that this demon had already set foot in the Central Capital, and Zichen Lake's arrangements to trap Evil Spirits were already tattered. If he felt that things were going badly and decided to act recklessly, releasing the control of all other Evil Spirits, the situation would become unmanageable!