Jim never refers to the island as anything other than treasure island, but treasure island is only the voyagers' private nickname for the place. Why doesn't Jim or Stevenson reveal a more geographically accurate name for this island? Does this name change

I think that Treasure Island serves more as an idea than specific geographical place. The Island can be seen to represent greed, adventure, pirate life, and brutality. These are themes and motifs that permeate the story. Giving the island a specific location would distract the reader from the allegorical and metaphorical aspects of the story.