As a broad generality, you're right about novelty being a poor criterion.

But in the specific context of the Nobel Prize in Literature... The Prize's official mandate specifies an author who has "in the field of literature, produced the most outstanding work in an idealistic direction". There's also a "for the greatest benefit to humankind" criteria.

With those ground rules, writing Yet More Books in well-trod genres - but just slightly better than any of the other authors there - really doesn't seem to cut it for the Nobel Prize.