Dan Bartlett, former White House communications director says this about the motivations of journalists,
I’ve found that most of them are not ideologically driven. Do I think that a lot of them don’t agree with the president? No doubt about it. But impact, above all else, is what matters. All they’re worried about is, can I have the front-page byline? Can I lead the evening newscast? And unfortunately, that requires them to not do in-depth studies about President Bush’s health care plan or No Child Left Behind. It’s who’s up, who’s down: Cheney hates Condi, Condi hates Cheney.
Whenever people complain about the left wing bias or the right wing bias of the media, I note that people respond to incentives. If the media is biased it is because that bias is popular. People want to consume that biased content. If people generally wanted totally unbiased media, that’s what they would get. It is difficult to complain about this because it is hard to see how it could be different.
I should also note that different media institutions have different biases. The media is not monolithic.
Via Matt Yglesias