While Christopher Tolkien's work through the HISTORY OF MIDDLE-EARTH series does a brilliant job of explicating all the various stages and how the multitude of texts relate to each other, the why must always be more allusive. Had Tolkien first written the Lost Tales in verse and then adapted them into prose, he would have been more closely following what I see as his primary model for THE BOOK OF LOST TALES, Wm Morris's THE EARTHLY PARADISE.
Each author has to follow his own muse, I suppose, and what a writer writes, and in what sequence, is often a complex interplay of internal and external forces. But while the other shifts in focus and genre make sense to me as I retrace Tolkien's career, this one doesn't. I can think up a lot of possible explanations, but none that really seem to ring true. So, for now, file this under "pondering". One day a little lightbulb may suddenly light up and all the pieces may fall plausibly into place, or this may remain one of those "Why? Because!" imponderables. I guess we'll see (or not, as the case may be).
today's music: "The Tourist" by Gerry Rafferty (dec'd.) [alas, not available on i-tunes]
today's audiobook: The Gospel of John