Tabloids have been making shit up about celebrities for decades. Brad Pitt has cancer! No, wait, he murdered a puppy! No, he kicked an orphan in the face! These things sell papers.
Then people realized the same thing works in politics: Hillary Clinton has cancer! She murdered a puppy! She kicked an orphan in the face! It's a proven formula, people click it, and you will make money given how things are monetized these days.
Attention, any attention, is something you can monetize.
That's the problem. Advertisers don't give a fuck. When they start to pay attention to where they're spending their money they might wise up and deprive these "fake news" sources of any incentive.