Why do creators invent new words for things that exist— and should they?
In my recent review of The Adventures of Peter Gray, I made a note that the book had furry characters which it termed furren. It is not something that I spent much time on but, in combination with some other reviews I've seen, it might be worth expanding a little.
During a review of Once Upon a Forest by The Nostalgia Critic, he noted that the children were called furlings. This lead him to ask, “Why is it fantasy films always have trouble just saying the word kids? It’s always furlings or younglings or Shia LaBeouf. Just call them what they are. Kids."
Similarly, in a review of Vampyr on Zero Puncuation, Yahtzee criticised using the terms ekons and skals for what were vampires and ghouls respectively.
Although to be fair to Vampyr, it does seem that ekon and skal are referring to specific subtypes of vampire. In such a case, it does make sense to use specific terms and it wouldn't be unlike the various vampire clans that feature in Vampire: The Masquerade.
The common issue that is brought up in all three reviews is the use of new word to describe something that already has a perfectly suitable word. Why is this done and is it a good thing to do?
When I asked Nathan Hopp, author of The Adventures of Peter Gray, about the term furren, he replied that was something he "wanted to use to distinguish my book from others within the fandom." Furthermore having a specific term which separated carnivore and omnivore anthros from humans and ferals "simplif[ied] my world-building but also helped me make my book distinct on its own."
So the first possible motivation is to make their work stand out. If you have unique terms, like furren or ekon, then anyone searching that term online will be more likely to find your specific work than anything else.
Another possibility, and one that Nathan Hopp also took into account, is that some terms can be copyrighted or trademarked. Certain companies leverage copyright laws aggressively to control aspects of our culture and go after other creators. At times, such copyrights are valid but in many cases they would be laughable if they weren't so serious. We've seen Zootopia released under multiple names due to copyright, Hasbro issuing a cease and desist against fan works and an author try to trademark the word "cocky." Disney is notorious for lobbying to extend US copyright durations from 14 years (28 if the author was still alive) to the current "life of the author plus 70 years" or, for corporate works, either 95 years from publication or 120 years from the date of creation. Ironically, most of Disney's animated movies were based on or adapted from public domain stories that had existed for generations.
That may explain, at least partially, the reason for the naming conventions in Vampyr. While the word ghoul has existed in English for quite some time, it comes from Persian and Arabic and refers to a corpse-eating demon. The use of ghoul for a being under the influence of vampire blood appears to come from Vampire: The Masquerade and is presumably copyrighted.
A third possibility for the use of a new term is because it really adds something new to an old concept. Many fantasy terms like elf and dwarf are heavily influenced by JRR Tolkien's work. To break away from that, one might want to use entirely new terms, even for very similar things. Of course, given that Dracula, The Vampire Diaries, Vampire: The Masquerade and Twilight all have very different conceptions of vampires and are able to use the term without people getting confused, I don't think this is a major concern.
But should creators do this? The answer is, of course, highly subjective and context dependent. I'm a lot more tolerant of using terms like furren or furlings in fantasy than if one just renamed a vampire but it remained exactly the same thing. It would not be enough to break immersion but when not engaged in the material it is something that I would find quite odd.
Due to the subjective nature of the question, I think it might be interesting to open the question up for debate. I have additionally created a Flayrah poll to gauge whether people think the practice is a good idea or not.