She told the Mail on Sunday that "it's difficult to explain why I didn't do it."
The singer added: "I prefer to do my charitable bit by donating actual money and not being lumped in a with a bunch of people like that.
"It's like the success club and I'm not really in that club. I don't think I'm above it all - I'm way below it. But there's something a bit smug about it."
The latest version of Do They Know It's Christmas? features acts including One Direction, Ed Sheeran, Jessie Ware and Rita Ora.
Within two days of being released, the song had sold 206,000 and become the fastest-selling single of 2014 and is on course to be number one in this Sunday's top 40.
However, Allen did go on to praise Band Aid organiser Bob Geldof saying "I actually don't mind Sir Bob" and that "he's grumpy like me".
Speaking to Newsbeat following the recording of the track, Geldof confirmed Adele hadn't snubbed his call to take part.
He said: "Adele won't pick up the phone to her manager. She's just out of it, which you respect. Nothing. She's not part of that anymore. That's absolutely her thing.
"Some people just don't want to do it, some people say no.
The singer's comments came less than 24 hours after Emeli Sande said "a whole new" Band Aid song is needed and that she's not fully satisfied by the lyrical changes made for this year's remake.
In a message posted on Twitter, the 27-year-old said she and African singer Angelique Kidjo "made and sang our own edits" whilst recording Band Aid 30.
She added: "Unfortunately, none of these made the final cut."
Later in the post, Emeli apologised "if the lyrics of the song have caused offence" but that the new version of the track "came from a place of pure and respectful intent".
Some of the lyrics have been rewritten for the fourth version of the charity single to reflect the track raising money for Ebola-hit west Africa.
The virus has killed more than 5,000 people in the current outbreak, including 1,267 in Sierra Leone.
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Lily Allen has revealed why she turned down an invite to sing on Band Aid 30.