Authors even Published ones can be lazy creatures of habit.
I am writing a Urban Fantasy Novel that may be never published. And yet like many before me and after me. I really done want to rewrite every little creature that may show up in my novel.
Maybe one day. I will be ready to create Bestiary of my own and either publish it or add it to the end of my novels. As I have seen some of the Masters do. I am not ready for that step yet. So for now RPG Game Companies make some money off me... They would have anyhow, as I am a that kind of Geek.
My answer, use creatures my most likely readers will recongize at some level. Am I copying every trait from these source books?? Of Course not!!!
After all the factions of my Novel do not match any of the factions in any of these games.
There are lot more beings and creatures that are of the Fey in my work for example!
On the other hand, if you know what a Drow is in D&D or 13th Age... You will recognize a drow in my world. Somethings are just so built into RPG and Fantasy .
Its a given that a Drow is a Drow, even if its not a evil selfish being surviving by serving something even more evil and much more selfish, then itself.