Because articles are now written to confirm people's preconceived notions. Articles that confirm your biases are more likely to be shared than articles which don't.
I honestly wonder if this writing style is conscious and intentional though, or rather un(sub)conscious and accidental.
Look at comments in forums...in that case, people have no profit motive, although they do have a "get upvotes" motive (so, virtue signalling is a legit motive, to some degree, but one notion to consider is that people very often no longer discriminate between that which is concrete factual and that which is inferred (imagined) "factual". If you look for it, you'll see that this behaviour is everywhere.
Oh, it's likely not conscious by the author. The most convincing of these one-sided views are the ones written by people who are "true believers" in their agendas.
Don't tell authors to take extreme stances, just ensure that stories get assigned to the ones that have strong views about the topic.
Even better, let the authors themselves decide what to cover. They will pretty quickly focus on their pet political propaganda and produce the click bait needed to drive eyes.
That actually makes a lot of sense....the desirable qualities for a journalist in 2020:
a) good/popular writing style
b) an ideologue in subjects that have high ideological "weight" in the population
Honesty, accuracy, fact checking, nuance, all of the traditional desirable attributes for journalists are now not only not required, but extremely undesirable.
And depending on the particular organization (say, a relatively reputable organization like the NYT), the only thing you need are editors who can proofread the article before publishing, replacing explicit assertions with a variety of weasel words, a big chunk of which could likely even be automated to insert suggested edits that just need a manual review.
Look at comments in forums...in that case, people have no profit motive, although they do have a "get upvotes" motive (so, virtue signalling is a legit motive, to some degree, but one notion to consider is that people very often no longer discriminate between that which is concrete factual and that which is inferred (imagined) "factual". If you look for it, you'll see that this behaviour is everywhere.