Because when the film was first mooted, the Beatles didn't like the idea at all. In fact they wouldn't have any part in it. And when Brian had committed them, it was part of a deal he did with United Artists, I think.

Ignatius College students were evacuated to Welwyn Garden City his family left London and he was enrolled at Bromley Grammar School. Pepper's Lonely Hearts Club Band)
Grammy Award 1973 – Best Arrangement Accompanying Vocalist(s) (as arranger of "Live and Let Die")
BRIT Awards 1977 – Best British Producer (of the past 25 years). He also composed and produced the film's score.

Following his graduation he worked for the BBC's classical music department then joined EMI in 1950. He is sometimes referred to as "the Fifth Beatle"—a title that he has described as "nonsense"—in reference to his extensive involvement on each of The Beatles' original albums. Martin produced comedy and novelty records in the early 1950s working with the likes of Peter Sellers and Spike Milligan.