There are a couple of different naming conventions, but I would definitely say that most of the successful settings do fall under the rubric of having been named for a concept, not a world.

Dark Sun, Forgotten Realms, Dragonlance, Birthright, and Al-Qadim all fit this mold.
Planescape and Spelljammer are similar, but they are also meta-settings so it is not quite the same.
Blackmoor, Greyhawk, Ravenloft, Nentir Vale, Kara-Tur, and Maztica, are all named for geography within larger worlds.
Eberron and Mystara are the main examples of the planet as setting naming convention, and maybe Ravnica? Eberron has done okay for itself with that name, and it may not have had much of a choice in the matter since "Dragonshard" and "Dragonmark" would tread on the toes of "Dragonlance" . But where does Eberron fall in the popularity rankings compared to Dark Sun and Ravenloft? And does anyone even play Mystara any more?

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