|Paul McCartney and Ringo Starr promo photo from the Beatles' "Let it Be" film, 1970|
According to the article:
One reason [for the delay] is that no work has been done yet on the mixing, remixing and so on of the original album, the original movie’s soundtrack, or the Peter Jackson documentary. The mixing sessions are set for this July. It shouldn’t take too long. At this point Giles Martin and his crew know exactly what they’re doing.
The other reason is that all these expensive packages will be aimed at a holiday release. They’re a waste of time in May for Apple Records and for retailers. If they come in October, they’ll be part of the Christmas shopping madness. It makes more sense all around.