In order to make Song Reader
feel even more authentic, Beck filled it out with fragments of songs and melodies and fictional album collections and song titles. "Why" is one of the fragments, for which Beck wrote a few lines. It is listed as part of a series of songs: "Who," "What," "When," and "Where" (but Beck did not write anything for those titles).
The sheet music has some fun comments on it like the first few lines are the "inquiry" then comes the "admission" and then the last "why oh" listed is the "lament."
With the somewhat clever turn in the two lines ("I never know why / It takes so long to find out why"), I'm inclined to believe this is all that Beck wrote and that there isn't more on the cutting room floor, so to speak.
The song's fictional publisher is listed as Fleischli & Turbin Inc. Michelle Ceazan-Fleischli is or was one of Beck's managers. Cassidy Turbin is one of Beck's main engineers who has worked on many of his recent recordings.