User blog comment:Zaarqawi/Why players from YGGDRASIL have been transported to the New World at various periods of time./@comment-27008999-20151110194334/@comment-27008999-20151111133336

Well the clues are when Ainz asked Sebas about if there was a floating castle in the sky in the first chapters. Ainz probably thought he was transferred to Middle-Earth or no longer in Helheim (ainz ooal gown's base world). 8GKs have a floating castle and possibly a world item (nameless spell book), which would make them very popular as anyone with a WCI rose in popularity quickly.