"So here's the question. If the media is so overwhelmingly liberal as the righties claim, why in the world wouldn't they be backing or at least featuring the most liberal candidate? The story is certainly compelling."

I would say if the media was less left leaning, they might be more interested in promoting John Edwards. And they would also try promoting Richardson. They promote Richardson by engaging him in serious issues. And after all he does have the most the most executive and governmental experience than compared to all the other Dem candidates- and even compared to all the Reps candidates he has at least as much if not more. But the media wouldn't help Edwards by dealing with any serious issue with him, because he is fluff and is essentially a greedy ambulance chasing lawyer who done well in terms taking money from health industry, but there no doubt that a lot poof pieces are possible in regards to spinning this lawyer's history: poor boy becomes rich by fighting the big evil corporations, and surely he spent some of his money or at least some of his time on some good causes, and these people he has helped, [with some professional speech writing help if needed], could given hours and hours of glowing reports regarding how good a person Edwards is.

Edward lacks substance- but media could if they wanted to attempt to give him some- though it's doubtful that not many people would tune in to watch this crap, not to mention the possibility of these type stories being "swift boated".

Now, to your question. The media wants to push for a Dem candidate who has best chance of winning against the Rep challenger. But the media also for reasons having little to do with liberal biases prefers an open race- the excitement of the horse race will boost their ratings. They will sell lots of newspapers [and TV] and this in general requires little in terms "work"- and it's going long and prosperous season. This race as it's turning out seems like it's going to be gold mine and all the reporters involved will gain much in terms of enhancing all of their careers.