Basically, the news is a presentation of the world, business-spun. There are two basic consumer publics. First the business world itself, second the ordinary public. And there are three structural layers. First is the broad structure of a constitutional democratic state and business-dominated society. Second is a market driven system. Third is a corporate structure. These will explain the content of the mainstream news and press.
The information that is presented, is always business-spun. For the most part, the essential facts are there somewhere, but presented from a business-spin perspective. This is distinct from a totalitarian propaganda model, where the picture of the world is just wholesale invented. Here you get the facts in there somewhere, but buried within a consistent world-view. For example, the US is freedom and justice, even when it massacres civilians. So you find out about the civilian deaths, but they are presented as collateral damage, their humanity is de-emphasized, they are only mentioned in passing, and the presentation justifies or defends the basic programs that killed them.
Second, inconvenient world-views are presented as snippets with business-spin. So when a world view or movement is large enough that the business community has to pay some attention to it, to react to it, then it is given air-time, but in the highly controlled manner described above. You have the presenter say, here is a really crazy dude about to say some really crazy stuff. Okay crazy dude, what is your worldview in 20 seconds? And then the presenter constantly interrupts or challenges what the now official crazy dude says. After the crazy dude is done talking and off air, the presenter says, well, now you’ve heard what crazy dude has said; make up your minds for yourself, but I think that guy is out of his mind and really quite disturbed to have those ideas…. The result is that the alternative worldviews and opinion-sets never have a chance to breath, to live on their own, even when there are large segments of the population who would normally like to hear them (as you would have in a community-controlled operation).
Market incentives structure news content as well by encouraging an infotainment model, and by subjecting news content to market forces as well as influence by advertising sources. Market forces encourage the news producers to run the most attention-getting, sensationalized, scandal-driven, simplified, lowest-common-denominator material, in order to maximize viewers/readers and turn a larger profit. On the other hand, since the profit depends on advertisers, these latter are given extreme influence, especially when acting in concert, over content. All advertisers have to do is threaten to withdraw their ads (or not to renew them), and the news producer is under strong pressure to comply in order to keep the revenue.
The fact that the media is a corporate structure means that those at the top of the corporate hierarchy have strong controls over content. The boss sends out a memo on how to cover topic x, and every recipient of the memo knows full well that their promotion, their raise, their bonus, and even their job depend on complying. This gives the corporate elite within the news producer complex a large amount of influence over content. If they don’t want something to be discussed, or they want it to be discusses in their direction not that one, they have the means to enforce their opinions.
But from the start, the systems of promotion in a business-dominated society are going to hold back anybody not sufficiently subordinate or indoctrinated, and promote those who “get it right”–who are adequately compliant and agreeable to those in control. This is from kindergarten onward. So you excel, and gain access to jobs and public speaking roles, such as journalism and press, when you have already gone through this two-decade filter system, virtually guaranteeing that you are going to be (since you graduated with a higher degree) “one of the good guys” from the business elite perspective. That is, that you have internalized a number of essential propositions (the state is good; our state stands for justice and freedom; our state can make mistakes but never commit real crimes; our state ought to be judged by its declared intentions and not its actions; our state is truly democratic; capitalism is essentially a decent system; etc.). If you were strongly against these and other propositions, or you were strongly adverse to authority, then you simply would not get promoted up through the system, not recommended for a job, would not get hired. There are occasional exceptions, people who learn to play the system, but only rare ones, which is what makes the system function well.
Finally, to clear up a misconception: the news does indeed have a liberal bias, and that is the point. The liberal bias of the news represents the limits of the spectrum of business-friendly thought. So while the right-wing opinion is ruthless anti-labor state capitalism, the liberal bias version (ie, the center) represents basic New Deal and neoKeynesian ideals. Anything left of the liberal perspective, such as socialist or anarchist viewpoints, cannot make it into the discussion.
The liberal bias on foreign policy: if we commit disasters, it’s okay bc it’s in the name of good. If you want to know what actual objective coverage would look like, it would cover our own (state) policies the same way it covers the state policies of official enemies (Russia, China, Venezuela, etc.). It would describe our own (state) crimes (slaughter of civilians, sponsoring terror, etc.) The way it covers the crimes of official enemies (Iran, Hamas, Hezbollah, Cuba, China, North Korea, etc.). If it doesn’t represent the Soviet invasion of Afghanistan in the same way it represents the American invasion of Afghanistan (or Vietnam, or Korea, etc.) In the same way, then we can see the extent of its bias.