The Makers poisoned Anara with Original Sin
Order legends hold that Kest was the one who "created evil", and even if it wasn't him specifically, something very significant changed when the Makers arrived on the scene. And through their discussions, they make it clear that "evil" doesn't just refer to organisms hazardous to humans but to the whole concept of evil. So in addition to bringing biospheric flaws, they must have brought a spiritual flaw as well. Now, there's very little we know about the Makers as people and therefore about any of their specific spiritual flaws, but we are quite certain they're humans, which means they are descendants of Adam and Eve and therefore carry Original Sin. Which needn't be present on Anara if the Sekoi never had a Fall. So they come and spill their corruption everywhere, their deep flawedness, their tendency-not-to-listen-to-God, and that's why nothing turns out properly for them.- Jossed. Original Sin can only be transmitted vertically, not horizontally, so it can't "infect" non-human species. They would have to perform their own sin.
