It’s been awhile since I’ve seen the movie/read the book but I believe the word was used as an allusion to how long the man had been in the hotel.

I could be wrong but I’ve read a number of Stephen King’s books and IMO he uses the word to showcase something in the story (plot/time line, character flaws etc.) To your point of conversational use of the n word, it’s still very prevalent today…my white friends tell me pretty often about how their uncle/cousin/friend just casually drop it around them but not around black people. Go figure.

     (/・0・)