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The new Arceus stories, when combined, literally explain everything about the underlying works of the Pokemon universe.
Think about it. What are the two main tenants of this entire franchise? Pokemon love to battle and Pokemon love human connection. Practically everything about how society and nature work in the Pokemon world finds its way back to these two main principles.
And we finally have the answer as to why.
What was the first thing Arceus did after being born? Literally fighting to the death and rapidly becoming more powerful (this is why levels and evolution are a thing).
And after it was defeated, what was the first thing Arceus experienced? Being cared for and nursed back to health by a human.
Of course God would create a world like the Pokemon one. How could it not, when those were the two most foundational experiences in its life?
Everything about Pokemon is Arceus' attempt at recreating the love it has for battling and humans. We now have been given all the answers. Do with them as you please.