In 1998, Walter Hooper, literary advisor of the estate of C.S. Lewis, was asked to summarize the legacy of Lewis and J.R.R. Tolkien:
Above all, they were both aware that the type of books they were writing were the type of books they liked to read. As Lewis said on one occasion: ‘I wrote the sort of books I did because they were the sort of books I would have liked to have read when I was growing up.’ When Lewis came across The Hobbit when it was being written he was delighted. This was not only the sort of book he would have liked to have read, but also the sort of book he would like to write. …
They were very honest men. They were not writing to be avant garde. They were writing books that they liked. They, after all, had jobs which left them free so they weren’t depending on writing stories that would sell. In some respects, Tolkien was reluctant to send his work to a publisher so you can hardly call him ambitious for that type of success. They merely wrote the sort of books that they liked which turns out to be the sort of books that many other people like.
From Joseph Pearce, ed., Tolkien — A Celebration: Collected Writings on a Literary Legacy, 2001. Of Middle-earth, Tolkien wrote in a letter, “I had the sense of recording what was already ‘there,’ somewhere; not of ‘inventing.'”