Ellen DeGeneres will not be on American Idol for Idol Gives Back

Rumor has it that Ellen DeGenees will not be co-hosting for Idol Gives Back. Sources of Access Hollywood said that the reason Ellen backed out was due to conflicting production schedule with her talk show. They report that they didn't know about the conflict until recently. Ellen was scheduled to tape the Idol Gives Back show on April 6th.
Hmm if she knew when she was going to tape the show, why didn't she plan ahead or said no when they asked? I wonder if there was another reason why she backed out?