Okay, since when did it become acceptable to become a heartless creature of the night in order to obtain immortality? Who wants to become a vampire, who can die from sunlight exposure, can't touch silver for the life of them, never again have most Italian foods thanks to an intolerance to garlic, and are unable to celebrate their beliefs because holy objects kill them? Also, who wants to be a werewolf, who basically has a three day period every month, need constant anger management, and are easily categorized as cannibals? Even being a zombie sounds like a bad idea as you'll be forced to eat brains for nutrition, become a mindless human eater, and slowly rot away into nothingness. Many authors think the lure of becoming some type of supernatural creature is enough to sell a story, which it is not. Why can't more stories exist where the protagonist instead of becoming a dark creature of some kind fights to stay human?

A great example of this trope is Circus Du Freak, a series of books where the protagonist Darren constantly fights to somehow stop himself from turning into a vampire. Although he ends up failing in his mission, it still makes for an interesting story, one we really don't see often enough in fiction anymore. A great internal struggle about fights with the literal demons inside of you creates strong potential for powerful storytelling. Just turning your character into the supernatural creature does not. Once they transform into the creature, all potential for strong conflict is flushed down the drain, usually not even halfway through the book. Sometimes this cliché can be played around with, such as is the case with most of L.J. Smith's vampire focused stories, which surprisingly includes The Vampire Diaries series of books. Conflict is possible to still exist, but you have to be a heck of a great writer to pull it off.