Part of the image she sells is the "girl next door"/"normal girl just like me" thing, so that probably leads to her fans thinking of her on a first name basis.

Part of the image she sells is the "girl next door"/"normal girl just like me" thing, so that probably leads to her fans thinking of her on a first name basis. It's very likely beneficial to her that people do. I'm skeptical about that in a lot of cases. For example, someone once pointed out that people called Spike Lee "Spike" a lot, where they never referred to Kubrick as "Stanley" or Scorsese as "Marty", and that there was likely a very subtle issue of respect there. That's probably accurate, and "Lee" is probably the more thoughtful choice there. But Lee, Kubrick, Scorsese, etc are selling an image of authority. Well, they aren't doing it themselves consciously, at least no more than any other director does as a matter of necessity. In any case, it's part of how directors are thought of, and Lee deserves that same kind of respect. Taylor Swift, though, is selling something different.