THEORY 1: VANITY FAIR HURT HER FEELINGS
Palin locks horns with the media on a regular basis, and the most recent addition to America’s Palin-bashing oeuvre—Todd Purdum’s 10,000-word Vanity Fair profile—was a doozy. Palin’s closest colleagues ridiculed her with nicknames like “Little Shop of Horrors,” accusations of incompetence and a personality disorder, and leaked personal emails. Alluding to Palin’s notoriously thin skin when it comes to media criticism (last week, an amateur blogger named “Celtic Diva” prompted Palin to ask for the president to intervene). Talking Points Memo’s Josh Marshall characterized Palin’s resignation speech as “a colossal sulk… an effort on her part to ingeniously combine anti-liberal media bias agitation with Christianist politics by portraying herself as having been crucified by the liberal media.”

And really, what better way to screw the media than making such a huge announcement on a holiday weekend? Gripes Politico’s Ben Smith: “So much for today being a slow news day.”