Our attention is the product for Facebook and Twitter. They make money by selling advertising. The more time we spend on the site, the more ads they put in front of us, the more money they make.
Outrage makes them the most money. We are more likely to share what outrages us. We have tribalized our social groups such that our friends are most likely going to be outraged too and more likely to share. So the outrages go viral.
The most effective things to make us share are also probably fake or misleading. We get so upset that we do not bother to check until maybe someone not so outraged fact-checks and points out the problem. So fake items go viral.
The synergy of fake outrageous news is powerful. It is manipulative. We train the social media algorithms that we WANT to be manipulated. We spend more time on these sites because we are addicted to being manipulated.