[Writing Prompt] What made it so that in Runeterra, all of the Skins are part of the normal world?

What made it so that both Kassadin and Pre-Void Kassadin can exist in the same universe, and even fight against one another. Why is it that Zilean decided to one day become a giver of gifts rather than sticking bombs into people? How can it be that Darius is both a Noxian soldier and a Woad soldier?

There are a lot of fun ideas to play with here, and I was interested in seeing what you fine ladies and gentleman would come up with. Go nuts!