This is a great question. The supernatural beings that were part of the belief system in pre-modern European tradition have been profoundly affected by modernization. First, they shifted from being entities that people believed in, described in oral tradition, to fictional characters featured in literature (and then in other forms of media). One of the more profound effects of this process has been to see various entities lumped together in modern stories, even if they were originally from separate cultures. In addition, some of the entities - giants and dragons for example - tended to be part of a remote past or a remote geographic location, while others including elves and their kin were something people expected that they could encounter in the lifetimes. By placing all of these entities together, they are from the outset far removed from the original tradition.

In the pre-modern world, the supernatural was dangerous. Encounters these entities could have terrible effect, and so people feared meeting supernatural beings. Legends provided guidance as to how to avoid encountering the supernatural and what to do if one had the misfortunate of encountering a supernatural entity. Literature tends to turn these entities into cute creatures or at least into characters that can be handled easily enough. And they gave fairies wings of all things! This is not something one would have found in Northern European folklore.

The following excerpt from my Introduction to Folklore may help:

At the end of the eighteenth century, various writers, most prominently the Grimm brothers, began publishing children’s stories based on folktales. These collections became extremely popular, particularly among the urban and increasingly literate emerging middle class as it found itself removed from the peasant soil that served as home to the stories. Fairytales often cause misunderstandings. In a culture that knows more about fairytales than Märchen (folktales), people assume that the folktale was intended for children. This is certainly not the case since the stories were often violent or sexual in ways thought inappropriate for children. Indeed, the telling of a folktale was usually delayed until the children had gone to bed. While fairytales provide the modern reader with the easiest access to the many stories that were once told internationally, one should always realize that they are removed from the primary inspiration. The original stories and their content provided serious entertainment for adults and they were part of an oral tradition, not something that was fossilized in writing.

The evolution of published fairytales had a profound effect on the subject of fairies, elves, trolls, and similar entities. Because fairytales became the literary domain of children, many people – including later writers – assumed the same was true of the supernatural beings. In their original context, nothing could be further from the truth. These were not cute, diminutive creatures whose sole purpose was to delight children. They were powerful, dangerous, and capable of great harm. The European peasantry feared and respected them, and their stories underscore this, conveying in uncompromising terms the code of ethics and behavior that one must employ to survive an encounter with the dangerous world of magic and power.