>>715919617
Because the universe was created by The First Ones and they decided how all the various realms of reality should work. They decided the afterlife should be split into five major afterlives and infinite smaller ones. They also apparently knew ahead of time it was all going to go horribly wrong and put contingencies in place to make sure mortals could fix it when it did.

Why they decided it had to work quite like that? We'll never know.