Because if she were to be the Chair of the GOP she would be beholden to the GOP 'insiders' and would not be able to say what she really thinks and endorse who she really wants to. The thing that makes Palin popular among the tea party crowd is her independence and her ability to say what she thinks instead of acting like a politician. That would vanish if she were to replace Steele. Mark my word, if she takes this position, her ability to draw crowds/support at Tea Party events will diminish instantly.