Lorde has recently told New York Times Magazine that, in her time living in New York, she has found that people just don't recognise her a lot of the time.
But I have another 'theory'. What if people do recognise her, but just don't go up and say hi (or say they want their photo taken, or whatever)? New York City (or any other city for that matter) is not a giant Lorde concert where everyone must be a fan of Lorde. I mean, if I saw Lorde somewhere, I would just leave her alone. It would be differnt if I saw Taylor Swift instead, but I just don't find Lorde that interesting (no offense, but people do see things differently). I am not particularly into her music, and don't know much about her otherwise. Why would I want to talk to her, a complete stranger?
I guess being a 'celebrity' and all that would make some people think that everyone wants to talk to them. But celebrity is usually the result of extensive media promotion nowadays, and being taught about someone's existence doesn't mean one would have any further interest in said person. I would think that most people who have been taught to recognise Lorde (or any other celebrity) by the media wouldn't suddenly want to talk to them as a result.
Maybe it's time that celebrities stop thinking and behaving like the world revolves around them. It's for their own sanity's sake.