Svaret är ganska tråkigt: Tolkien tyckte inte om tanken.
Peter Jackson, som direkt en lite bättre känd filmanpassning, träffade Paul McCartney vid Academy Awards 2002, där han lärde sig om dessa planer. Han kommenterade ett New Zealand-papper :
Jackson, whose own version of the first book in the fantasy trilogy, The Fellowship of the Ring won four Oscars this week, told the newspaper that the Beatles plan fell flat when author J.R.R. Tolkien rejected the plan. […]
“[The film] was something John was driving and J.R.R. Tolkien still had the film rights at that stage but he didn't like the idea of the Beatles doing it. So he killed it,” Jackson told the newspaper.
Matthew Schmitz har en artikel på Första saker har skrivit lite mer om planerna och har ett rimligt gissning för varför Tolkien kände sig vild mot Beatles:
In a 1964 letter to Christopher Bretherton, Tolkien complained about “radio, tele, dogs, scooters, buzzbikes, and cars of all sizes but the smallest” making noise “from early morn to about 2 a.m.”
“In addition,” Tolkien wrote, “in a house three doors away dwells a member of a group of young men who are evidently aiming to turn themselves into a Beatle Group. On days when it falls to his turn to have a practice session the noise is indescribable.”