because the constituencies involved (of both the characters in the book, and the modern audience that consumes them) prefer the absence of a strong federating remote figure, to the ability of being able to imprint/insert themselves as participatory observers of the events.

lack of a strong central nexus gives fantasy writers and readers the opportunity to engage with the story and period on their own terms, instead of being subjugated to what some accidental monarch wants the era to have been.