The Boomtown Rats singer rallied stars including Bono, One Direction, and Ed Sheeran to re-record his 1984 track Do They Know It's Christmas? last month (Nov14) to raise funds to fight the Ebola crisis in western Africa.
He has faced criticism for not asking the Beatles star to take part in the charity single but insists it was a fair decision as MCCartney was in the 2004 version, Band Aid 20.
Geldof tells British newspaper the Daily Mirror that he wanted current stars to feature on the track.
Asked why MCCartney wasn't involved, he replies, "Because MACca's always done stuff. He was in the band in 2004 - him, Radiohead and Damon (Albarn). But look, on this we've got from the newest to the hippest to the oldest... and he hasn't made the cut, what can I tell you? The thing is, there's only so many lines, so what do you do? At one point Midge Ure was like, 'We can't take more', so you try and make it the girls and the boys, that's the first thing.... Then it's who's happening in America - that's really important as sales are quantifiably more over there. Ellie Goulding, Ed Sheeran, One Direction, Coldplay, Sam Smith, U2... all these people are caning it in America."