As the Countess of the Banished Dark Moon mentioned, the collective attack from the other Lunirich Gods that was directed at Rex, transcending the barrier between the God realm and the mortal realm was not done without repercussions.
It was a direct attack from literal Gods, which was unbelievable.
Only a few instances in the past could match the level of what the Lunirich Gods did to Rex.
Gods shouldn't interfere in the mortal realm directly.
Sending a celestial envoy is the normal way of connecting with the mortal realm that will not cause a heavy backlash on them. But it's true that the celestial envoy will only retain a small portion of the associated God's power.
Naturally, Rex should've seen this coming.
In a twisted way, breaking the Lunirich Edict is him interfering with the matters of the Gods.
Surely, the Gods would return the same thing to him.