Why are fairies cruel?

  I've just read A Court of thorns and roses by S J Maas even though it was published in 2015.

It reads like an adult fairy tale and like the fairy tales I hated in my childhood, it is in part gruesome. Now I don't mind so much. I'm big and grown up and I can handle gruesome. But why is this sort of fantasy suddenly so popular?

The Sunday School I used to attend pre the age of seven gave out copies of Grimm's Fairy Tales as prizes - I can't remember what for. I got one, and when I began reading the short stories  they had me in tears so often that my parents took it off me and hid it somewhere. Or threw it out - I don't know what they did with it to be honest.

I wonder why fairies are thought to have this streak of cruelty? Ms Maas's fairies are definitely cruel. I might even say downright sadistic. Maybe it is as simple as a corruption of power. Give someone enough power and they will use it - whether it depends on good or bad depends on the personality of the individual. If you have any good ideas as to why fairies are cruel, let me know!