Towards the end of his career, J. R. R. Tolkien faced many obstacles both internal and external that stood in the way of his finishing and publishing The Silmarillion. This paper explores the various elements that contributed to his dilemma and concludes that the key factors were twofold.
First came the traumatic breakdown of his efforts to publish the book through Collins, leading to a catastrophic interruption of his work on the book.
In addition, by this time Tolkien had concluded that many of the most iconic elements in his mythology could no longer command evoke secondary belief in modern-day readers. His unique cosmology inspired some of his finest writing, yet in the end the Flat Earth/Round Earth dichotomy became the most intractable of the problems facing him as he strove to find a way to finish The Silmarillion.
In the end, this led him to an impasse wherein on the one hand he had concluded he must make a major change without being able to bring himself to do so.
Rateliff, John D.
""The Flat Earth Made Round and Tolkien’s Failure to Finish The Silmarillion","
Journal of Tolkien Research: Vol. 9:
1, Article 5.
Available at: https://scholar.valpo.edu/journaloftolkienresearch/vol9/iss1/5