Deena Skolnick Weisberg writes up some interesting research that (provisionally) suggests that children learn certain kinds of information better from fantasy writing than realism:
A different, and richer, possibility is that there’s something about fantastical contexts that is particularly helpful for learning. From this perspective, fantastical fiction might do something more than hold children’s interest better than realistic fiction. Rather, immersion in a scenario where they need to think about impossible events might engage children’s deeper processing, precisely because they can’t treat these scenarios as they would every other scenario that they encounter in reality.
They must consider every event with fresh eyes, asking whether it fits with the world of the story and whether it could fit within the laws of reality. This constant need to evaluate a story might make these situations particularly ripe for learning.
My hypothesis is that we are creatures of story. Story can take control more clearly when unmoored from all the constraints of our specific reality. But it can't go too far.
"She was obsessed with getting through the asteroid belt faster" focuses me on the story more than "She was obsessed with getting through the car wash faster", but also more than an obscure sentence like "She was obsessed with getting through the Andromeda Nexus in fewer light years".
The right amount of novelty seems to help. And the novel scenarios of sci-fi can mean that every detail alludes to so much background story. Everything is new, except the background associations and history we bring to the story. So there is a mutually reinforcing power to the figure and the ground, to borrow a phrasing from Gestalt psychology.
In Star Wars, Luke gasps "You know about the rebellion against the empire!?", and we know that it's kept hush-hush, that he sympathizes with it, and that it strikes him as daring in contrast to his mundane agricultural existence. We are bringing an immense amount of knowledge to that line, but it is able to cast a shadow without being encumbered by our knowledge.
Adding to that, since the scenarios are concocted from whole cloth, they can use bolder stitching. The galaxy can be in a rebellion that has a murky religious battle underneath... the stakes can be so high.
I recently reread CS Lewis's The Voyage of the Dawn Treader to my daughter. It opens with a conservative takedown of what was then considered progressive education. Eustace, a schoolboy at such a school, is a jerk who only reads about real things--grain silo capacities and such--and is taught to look down on fantasy. Meanwhile, of course, the whole series is an argument for the power of fantasy to communicate about Jesus better than the church does.
From the last chapter of Dawn Treader:
"Dearest," said Aslan very gently, "you and your brother will never come back to Narnia."
"Oh, Aslan!!" said Edmund and Lucy both together in despairing voices.
"You are too old, children," said Aslan, "and you must begin to come close to your own world now."
"It isn't Narnia, you know," sobbed Lucy. "It's OK. We shan't meet you there. And how can we live, never meeting you?"
"But you shall meet me, dear one," said Aslan.
"Are—are you there too, Sir?" said Edmund.
"I am," said Aslan. "But there I have another name. You must learn to know me by that name. This was the very reason why you were brought to Narnia, that by knowing me here for a little, you may know me better there."
It is a powerful argument for illumination through fantasy.