Bluebeard is a fairy tale that essentially tells a story about a serial killer who is testing his wife with the key to a forbidden room. She has a tool to unlock it but is forbidden to do so. She also knows her husband was married several times (in some versions six, in some eight) before, but all his spouses mysteriously vanished.
https://brinsley-le-fanu.mystrikingly.com/blog/bluebeard
When she can't resist the temptation, he decides to kill her, just like all his previous wives. But fortunately for her, her sister calls for help and two brothers of the condemned wife return just in time to kill the Bluebeard, secure her a huge inheritance and the story ends with some kind of happy end.
Well, this story was among the most popular ones in the 18th, 19th, and first decades of the 20th century. Today it's almost forgotten and very rarely at least included in collections of classic fairy tales. Why? Because the title character is so strange? There are many other popular tales with unconventional characters.
A blue beard may look out of this world but the same is true, for instance, for Rapunzel's extremely long hair or, if we stay limited to particular personal characteristics, Goose Girl's golden-colored hair.
The cruelty in the story should not be the reason for falling out of popularity, because in Hansel and Grethel we deal with cannibalism, infanticide, and burning the wicked witch alive in her oven. Cutting parts of Cinderella's sisters' feet or dancing in the hot iron shoes of Snow White's stepmother belongs to the same category. Cruelty is an important part of fairy tales and Bluebeard is not an exception.
My theory is, although, a bit controversial, that Bluebeard lost its shine due to something different - globalization.
When Charles Perrault published the first collection of modern fairy tales (Bluebeard being one of them, the world was different. There was a clash between the Christian and Muslim religions. While the only description of Bluebeard is the color of his beard, illustrators immediately started portraying him in typical Muslim attire. He has a turban, wide pants, and a scimitar. He obviously comes from a different cultural and religious environment. Due to the many wars between Christian and Muslim religions, he is clearly presented as an enemy.
https://yesterdaysdream.hatenablog.com/entry/2020/05/14/084229
The other important detail is the naming of both sisters. Fairy tale characters in most cases don't have names. They are called by some characteristic (like Snow White, Cinderella, or Red Riding Hood), or profession (miller, tailor). Even if they have names, it's always generic. In the collection of Brothers Grimm, we can find dozens of characters with the name Hans or Grethel.
But not in the Bluebeard. The sisters are named Fatima and Anne, both very popular names in Muslim or Christian environments for centuries. Fatima marries Bluebeard and is passive, and weak, but Anna, although barely important in the beginning organizes the rescue of Fatima, when she confronts the death threat.
https://charles-perraults-fairy-tales.weebly.com/fairy-tales/bluebeard-by-walter-crane
Numerous wives of Bluebeard insinuate polygamy, which was usual in the Muslim world but not among Christians.
So we can interpret the fairy tale of Bluebeard as a danger presented to Christians by the Muslims and the final win of Christianity. The ending, when Fatima gets her husband's possessions, is somehow controversial. Women were not inheriting properties at those times. Even when a husband died before the male heir was born, the inheritance was just formal. In reality, brothers, fathers, or other male relatives controlled the properties.
In the fairy tale of Bluebeard, this is solved with the arrival of brothers at the scene and a quick marriage with another man.
Today, such a presentation of relationships between men and women is outdated. This, in my opinion, is one of the main reasons why Bluebeard became outdated as well.
And what do you think?