I'm a fan artist myself, but I'm not one of these. I deal with them all the time and they are indeed irritating. My fan art intentionally has my own version of the official character style and I always redesign a character in my own way (it is "deviant", after all). But there is always one of more fan piranhas who will then come and tell me something about the physical appearance of my fan art is "wrong" or "inaccurate", even though it was my intention to do it differently.
It might be for this reason that most fan artists (unfortunately) try to replicate the exact style and portrayal of the characters they are fans of. Unless the character(s) are doing something interesting in the art, I find this incredibly boring and repetitive.
They don't realize that "fan art" means a fan's own representation of something they like, not a replication of it.
I appreciate this! You are a very good observer of the community here!
*loves this so much* Every time I find a fandom, I turn around and find it descending into popularity. (I read and adored the first Harry Potter book when it was originally published, and two books later I was lost under a sea of enthusiastic eight-year-olds and Bible-thumping angry parents....) I can't decide if I'm a trendsetter or an albatross.
I was very recently one of the Backyard Trees (or possibly a Hmmmicorn) and then a horde of Fan Pirahnas and Wow Birds swarmed my page... Yes, this describes them perfectly. Fan Pirahnas, lol, I'd never have thought of it!
I quite enjoyed this dA Bestiary of yours. It made me giggle incessantly and your artwork brings to mind fond memories of joke cards and MAD magazine. ^_^