The explanation that I usually read is that it's a cultural phenomenon, that within Chinese culture in particular, people are more inclined to describe others as inhabiting various roles instead of having persistent character traits (with this being reflected in some older Chinese literature and philosophical traditions) - but this is mostly just a vague impression I have that was probably formed by reading blog posts by people who don't really know what they're talking about, so take this with a grain of salt. ;)

An amusing bit of trivia: among the Japanese nobility at the time The Tale of Genji was being written, referring to someone by their name was a privilege reserved for family and very close acquaintances (and not something that would be appropriate to do in public), so all the characters in the story are referred to by titles and descriptions of various kinds - and these "names" change when the characters end up in different life circumstances.