Why the Beatles didn't voice themselves in the Yellow Submarine movie adaptation

In 1968, the Beatles were riding the mighty crest of the psychedelic wave. In case the audiences had somehow managed to miss the formerly squeaky-clean Fab Four's transition to facial hair, colorful costumes and Sgt. Pepper's Lonely Hearts Club Band, the full-length, Beatle-themed animated movie Yellow Submarine certainly drove the point home. The movie is a curious cult classic that sees the band joining a man called Old Fred in his yellow submarine, and traveling through many strange seas to free the fantastical Pepperland from an occupying force of evil, music-hating Blue Meanies. All of this, of course, is (Sgt.) peppered with copious amounts of Beatles songs and weird, innovative psychedelic imagery that elevated Yellow Submarine above and beyond a mere "movie about a band." 

As such, it's only natural that the movie's versions of John Lennon, Paul McCartney, Ringo Starr and George Harrison were voiced by none other than ... uh, John Clive, Geoff Hughes, Paul Angelis and an uncredited dude called Peter Batten? Wait, what? Why didn't the Beatles voice themselves in what's arguably their best-known movie?

The Beatles were too busy to voice themselves, but regretted it afterwards

As Lina Lecaro of LA Weekly tells us, there was a very simple reason for the Beatles to be absent from the speaking roles of Yellow Submarine. All four of them happened to be in the most famous band in history at the time, and as such, their schedules were quite hectic — apparently, way too hectic to take time to record their lines. However, hindsight being 20/20, the band members have stated multiple times that they regret not going all in with the film. 

Still, it's not like the band's completely absent from the movie. Being the Beatles, they obviously sing all their own songs. In the very end of the movie, the viewers are also treated with a live-action scene of the Fab Four, which sees George Harrison, Paul McCartney and Ringo Starr proudly showing us the various whimsical souvenirs they claim to have brought back from their submarine adventure, before a telescope-wielding John McLennon proclaims that a batch of even worse Blue Meanies have been sighted outside the movie theater. Unfortunately, this nifty sequel hook never turned into a White Album-themed Yellow Submarine 2: Everybody's Got Something to Hide Except Me and My Monkey.