No, you're right. There are time when that'd work. A fic from Draco Malfoy's POV might very well say "the Mudblood" instead of Hermione or something. I just usually see it used in a "I don't want to say George" again way, and it makes no sense for the POV character to be thinking about her friend as "the brunette boy" or whatever. In one of my fandoms, they often said, "The curly haired rebel" which could refer to four different characters for instance. They used the professions of other characters for other epithets. That just comes off as a bad writing, and some sort of weird name-avoidance.