Perhaps it has something…
Perhaps it has something to do with the fact that “faith” was once counted among the cardinal virtues?
“Where [is] the wise? where [is] the scribe? where [is] the disputer of this world? hath not God made foolish the wisdom of this world? For after that in the wisdom of God the world by wisdom knew not God, it pleased God by the foolishness of preaching to save them that believe. … But God hath chosen the foolish things of the world to confound the wise; and God hath chosen the weak things of the world to confound the things which are mighty; …”
This is not to say that the theme of “just believe” in children’s fantasy is an intentional or even an accurate expression of the purported theological virtue. Or that people were right to regard this kind of faith as a virtue to begin with. But I do think that this obviously has to be part of the correct explanation.
Anticopyright.