Premodern people--both pagan and Christian-- also valued the "right brain" as much as the "left." That is, they didn't limit rationality only to discursive reason. Truth was not just a quality of propositions, but of things themselves, which participated and mirrored the Truth beyond them. T
Thus, Tolkien also connected fairy stories with "freedom from fact." But modernism is by definition consumed with facts. In Dickens' "Hard Times," Mr. Gradgrind, the school superintendent is a model of modernism. He declares, "Now, what I want is Facts. Teach these boys and girls nothing but Facts. Facts alone are wanted in life. Plant nothing else, and root out everything else. You can only form the minds of reasoning animals upon Facts; nothing else will ever be of any service to them.”
American literature is "realistic" because America was born in the Enlightenment, and has modernist DNA. Our focus is on THIS world, not any other. As such, it is "flat," anti-sacramentalist, and consumed with "facts." No wonder our children's literature is so pallid and ordinary in comparison to the Brits'.