Fable or Fairy Tale?
There can be no good fable with human beings in it.
Consider the fable of the fox and the goat. The former fell into a well and was unable to get out. And then a thirsty goat came along. The fox coaxed him. When the goat quenched his thirst, he was told to lean on the brick wall and let the fox climb up. This familiar story would teach readers the moral of looking before leaping, but it won't be a strong message if humans were there instead.
Some readers might think that the author was being judgmental. They have a point, as it would be impossible not to be compassionate towards the fox. And the goat couldn't be faulted for the good deed he showed. But the fox and goat were abstractions in this tale, which made the moral loud and clear. A good fable is a rarity nowadays. In fact, this was often heard during ancient times. It seemed hard to believe, but a Greek myth and a fable featuring animals were on the same level.
A good fable, like an epic myth, was told to entertain audience. It was part of oral tradition, a culture long gone and rediscovered. It would be hard to tell if there was a factual basis behind the fables. Some won't press its authenticity, assuming these tales were make believe. And they have a point. (The Olympian deities were nothing more than imagination of ancient Greeks.) So why did these tales fascinate modern readers? They were simple yet effective. There was no pretense, not even beating around the bush. Some adult readers may be jaded not to follow the morals of these fables, but they should. Some stories were meant to believe.
There can be no good fairy tale without humans
A fairy tale, on the other hand, won't endear to readers if there's no heroine to root for and a villain to go against. This is the case of Sleeping Beauty, who didn't do wrong to a fairy who wasn't invited to be her godmother. She was hardly conscious of the curse that sealed her destiny, which made readers hoping she won't prick her finger.
Fairy tales don't have morals, but they might be drab if animals were in place of humans. Furthermore, the story might be less interesting if a male was the lead character. Not that the authors of these tales were guilty of misogyny, insisting that women were the weaker sex. It was a universal truth that female protagonists could attract more readers than their male counterparts. It would be unfair, but such was the state of fairy tales back then. And they don't make such stories anymore.

