They're trying, to some extent, to broaden the base beyond the obvious: a boy eats something and begins to understand animal speech, a group of men are turned to swans by a woman who threw shirts at them. Still, these tend to be backdrops and minor figures, often nothing more than local color. Front and center, you have the old standbys. Which produces a self-reinforcing system.
You can't blame them entirely, since the old standbys are indeed all that some readers know. I have read myself a description of strange and unusual folklore, that picked out that in the Chinese fairy tale "Ye Xian", the Cinderella figure is helped by a fish sent by her dead mother. (wince) You don't have to leave France for a Cinderella figure helped by something from her dead mother. You just have to step over the border to Germany, where the Brothers Grimm will tell you about Aschenputtel, whose assistance comes from a tree planted on her mother's grave and the doves that perch in it. It is, in fact, the standard European way of telling the story. Perrault is the odd-ball, with his fairy godmother.
Indeed, if I were discussing Ye Xian, what I would point out is that the king who marries her isn't at the festival where she loses her shoe. He finds out when the shoe travels from hand to hand and ends up with him, whereupon he falls in love with the woman who could wear that. Though I would more likely have chosen "Beauty And Pock Face", where the beauty loses her shoe in the ditch trying to get to the ball and refuses a number of men's aid at the price of marriage until a scholar is the one who makes the offer. (Her stepsister then kills her and substitutes herself for her after the wedding, claiming she had had smallpox, and the beauty comes back in many forms to stop her -- but that's also a commonality with European tales. It's the ditch that's unique in my experience.) That is, if I had to choose a Cinderella tale. I more likely would have gone for, say, Madame White Snake, with the romance between a man and a snake that turns into a woman. One notes that is her backstory. In European tales, an animal lover that transforms to human was originally a human, or a fundamentally shape-shifter sort at heart, like a swan maiden or a selkie. In the Far East -- Korea and Japan as well as China -- an animal really can learn to become human, through Taoist arts or merely long life.
But, as the case of Aschenputtel shows, you do not have to go that far afield. If you want read strange fairy tales, go to the fairy tale section of the library. Do not pick out a thematic collection, especially not of Cinderella variants. (fine if you want variants, not if you want strangeness). Do not pick out a collection of fairy tales about the world, though they can be better. Pick a collection of fairy tales from a country or region. And it does not matter which. Even though the known fairy tales are generally French (Cinderella, Bluebeard, Beauty and the Beast), German (Snow White and the Seven Dwarfs, Sleeping Beauty, Little Red Riding Hood), English (Jack and the Beanstalk, Goldilocks and the Three Bears), and Norwegian (Three Billy Goats Gruff), the collections from these countries contain scores if not hundreds of tales. Even when you recognize the tale, it can have a strange fillip to it. Joseph Jacobs included a tale "Scrapfoot", which would be "Goldilocks and the Three Bears" except that the main character isn't even human, he's a fox.
Come to think of it, there's another advantage to it. If you read English, German, French, and Norwegian tales as well as Chinese, African, Haitian, etc. ones, you are less likely to think that any given motif or tale is non-European when that's not justified.