neo-Conservatives have dominated the far-right and pushed everyone over so that traditional moderates are now Leftist guerrillas.
The majority of the population has now become 'Liberal', including the old sensible Republican. So why should an open system like journalism be immune to this shift? After all, these people are not seperate from the societies they part of...
The other reason is because the money-men, your Blacks, Aspers, Scaifes and Murdocks who dominate the massmedia hire right-wing editors and management. It's the Golden Rule. He who has the Gold, makes the rules. For the most part, these yes men prevent investigative journalism, pushed for feel-good/feel-bad 'human interest' stories to replace them.