I still don't buy the idea that having different settings "fractured" the D&D player base: no one I ever knew refused to buy Forgotten Realms or Ravenloft books because they "only played Dark Sun." Yes, people may have had favorite settings that they focused on, but everyone always bought everything they could in my experience, and ran multiple games in different worlds, including homebrew which they would fill with ideas cribbed material from all the books. Just because Greyhawk was my favorite didn't mean I didn't also buy up Drow of the Underdark and Dragon Kings the moment I saw them, or consider The Code of the Harpers to be one of the best and most interesting D&D books I've ever owned and still crack open to read through today.
Producing more books than they could sell is what killed TSR, not having multiple settings.
Producing more books than they could sell is what killed TSR, not having multiple settings.