Source of funding is the key. Social media enabled the idea that news could be free, and that's where the dominoes started falling. The signal to the news company is that they need to keep pushing out articles which people click on or share. The incentive of reputation and prestige got replaced by click-baity and virtue signalling.
True to some measure, but not completely - there are still degrees of click-baity-ness and not all media companies are like buzzfeed or gawker and publish exclusively in the style of "15 reasons why your biases are completely justified and anybody who disagrees with you are evil, #8 will shock you!". There are media companies that make conscious effort to do better - it's just they think that doing better means shaping the news to help the audience to arrive to "right" conclusions. They think this is their social responsibility, not to inform, but to form "good" opinions and to destroy "bad" ones. Combined with natural grouthink that arises in organizations having no focus on thought diversity (which are pretty much all news orgs) it produces a very distinctive mindset, which, as I noted in other place, is not just about money - it's about doing what they genuinely perceive as the right thing.
In essence, they think the masses are too stupid to be fed bare truth, and need to be put on a carefully selected diet of curated truths, half-truths and sometimes outright lies, in service of a noble goal. I'd like to have the informers back instead.
