After learning about the changes in the Silver Moonlight Festival, I've spent some time researching it, using my resources at both Vera and the Basilisk Order libraries. But the most trusted information actually came from Seraphiel himself.
According to the Archangel who once fought alongside the Great Gods, before and during the initial war period when the Demons invaded, the Gods often organized challenging Trials to select their champions who could later become the true heroes of this world. If chosen, one would receive great blessings and be granted some of the best artifacts in the entire world. Compared to the Second Ocular's Treasury, the sheer number of artifacts that Luna's Domain holds can only be greater, not less, with some even dating back to the beginning of this world.