As early as when the God of Sun and Evil Fire had just appeared, Garen had sensed something unusual and immediately returned to the Royal Court to enter the Hall of Eternal Heroes.
At the center of the Hero's Domain's core, Garen, the Lord of Heroic Spirits, was continuously absorbing life force to restore his state to its peak. After all, he had previously sealed the Lightning Snake and the Starlight in his twilight years, and his own consumption was not small.
If he descended to the prime material plane in a bad state, there would be too many variables.
Moreover, the God of Light was not completely defenseless, so Garen did not immediately descend to assist the God of Light.
In the Pantheon Temple, the incarnation that Garen left behind had also communicated with the incarnation of the God of Light, asking the God of Light to stall for as much time as possible so that Garen could absorb life energy to replenish his state.