Tolkien was Catholic. Lewis was Anglican. Neither of them gave much credence to Calvinism. Part of it shows right here I think. Their own philosophy about the value and beauty of myth-making and storytelling does not jive with the doctrine of total depravity, at least, not with a lot of qualifications.
Tolkien said, man is not ultimately a liar. He may pervert his throughts ito lies, but he comes from God, and it is from God that he draws his ultimate ideals. Lewis agreed: he had, indeed, accepted something like this notion for many years. Therefore, Tolkien continued, not merely the abstract thoughts of man but also his imaginative inventions must originate with God, and must in consequence reflect something of eternal truth. I making a myth, in practising ‘mythopoeia’ and peopleing the world with elves and dragons and goblins, a storyteller, or ‘sub-creator’ as Tolkien liked to call such a person, is actually fulfilling God’s purpose, and reflecting a splintered fragment of the true light. Pagan myths are therefore never just ‘lies’: there is always something of the truth in them.
-Humphrey Carpenter, The Inklings, p.43