But first, it's interesting to take a look at which news sources are trusted and distrusted by Americans. Pew put together this handy infographic, which reveals that the Wall Street Journal is the most-trusted news source and, by ratio of trust-to-distrust, Buzzfeed is the least-trusted (also, that nobody knows what ThinkProgress is):
[Addendum: No Townhall? For shame, Pew.]
One of the takeaways, according to the Pew analysts, is that "consistent liberals name an array of main news sources," while "consistent conservatives are tightly clustered around one main news source":
This makes for an easy talking point by those who would like to resurrect the old "epistemic closure" debate: look, conservatives all listen to Fox News! They don't get their news from other sources! But this is incorrect - this is only about main news sources. It turns out that people who reported as being of a "mixed" ideology - neither liberal nor conservative - have the most sheltered news lives:
This largely fits with what we know about political independents: they're either secret partisans or they're just low-information. A Pew survey from 2012 found that independent-aligned voters were consistently less-informed than their Republican or Democrat counterparts.
When we actually take stock of the ideological profiles of different news organizations, this makes sense: liberals have many many more outlets to turn to in order to get their news! The reason we have a "conservative media" at all is that non-ideological liberals were upset at what was perceived to be a consistently ideologically-liberal media. CNN has a reputation for centrism, but it's still perceived to be more center-left than center, judging by its audience. For a long time, conservative news consumers had only Fox News in order to get news. There are slightly more "conservative" news sources now, but if we take a look at the ideological audience profile that Pew put together, "consistently liberal" audiences have more than double the news sources to go to than "consistent conservatives."
A liberal might respond that, well, of course this is the case: liberals care about news, conservatives care about spin, and that "reality has a left-wing bias" (or whatever that phrase is supposed to be). But that's largely a cover-your-ears answer to the problem of media bias and a rejection of the actual problems that plague the news industry. Fox News and other conservative sources might not adhere to the view-from-nowhere standard of old-media journalism, but critics both left and right have pointed out that view-from-nowhere journalism is just a way of denying an existing bias rather than combating it.
Even in the wake of the Fox and new media revolution, it's true that conservatives simply have much less choice in news than liberals. Given that, it's unsurprising that they tend to "cluster" around one giant news source.