As Katie Couric's tenure as anchor of the CBS Evening News draws to a close, the question remains: what went wrong? Why couldn't the former Today show host break the broadcast out of its last place ratings rut? In the hours before her final broadcast, we present some of the more promising theories.

She was too sunny! Viewers don't want happy anchors. They want an anchor who is serious, sober, and thorough. It didn't even matter that Couric was all those things, says network TV analyst Andrew Tyndall. He tells the Los Angeles Times' James Rainey that under Couric, CBS outpaced ABC and NBC in minutes spent on hard news news stories. It didn't matter, writes Rainey. She could never shake the "morning-lite" image of Today.

She wasn't 60 MinutesHer own network is taking the position that Couric's Evening News was too fluffy. At CBS upfronts yesterday, her image was noticeable absent from promotion material. Even Anderson Cooper made it into a montage, notes Brian Stelter. When he took the stage, chairman Jeff Fager promised advertisers that the Evening News would have "new energy and a new direction" under Scott Pelley. But what sort of new direction? Narrating his sizzle reel, Pelley offered a clue: "What if you could watch a program that had the integrity, reporting and insight of 60 Minutes every weeknight? Well now you can.”

She was too liberal! The Sarah Palin interviews were the unquestioned highlight of Couric's tenure, but they also established her as a right-wing villain. (The leaked footage of her pre-relase preparations for the interview, embedded below, didn't help, either) Palin gloated when the departure was announced, "I think I read that in a newspaper." The Media Research Center presented a list of quotes that illustrated her "infatuation with liberal politicians and her chirpy promotion of left-wing policies" that was widely circulated in the conservative blogosphere. Among the more innocuous comments that belied a secret agenda:

  • "Maybe we need a Muslim version of The Cosby Show"
  • I think providing health care for people who can’t afford it is something that most people do agree with — that there has to be some kind of alternative other than our national, our nation's emergency rooms for people who need health care"
  • [To John Boehner] "Do you think the Republicans are digging themselves in a hole by not being more supportive of the President’s proposals?

She had a bad start! An unnamed CBS executive says the changes made to the program's format upon Couric's arrival (more interviews, special guest commentaries)  were "a shock to the system" for viewers used to Walter Cronkite and Dan Rather. By the time they went back, the audience was already gone. "The week she started, the tune-in was huge," says the executive. And the drop-off was also huge after that. I don't think they were ever able to get them back."

She didn't fail! Editorially, the Evening News under Couric was a success, winning the Edward R. Murrow for best newscast in 2008 and 2009 and the Walter Cronkite Award for its coverage of the 2008 presidential race. And it's not like she was fired. She's leaving with just two weeks left on her original five year contract. And she'll always have that Sarah Palin interview.