The algorithms primary objective is to generate interaction.

Interaction leads to ad revenue.

The quickest and easiest way to get people to engage with a topic is to infuriate them.

After all, how many of us have apps on our phone that shows them only cute pictures of cats and dogs and babies?

How many feel-good stories do you read in an average day?

How many of us spend our time solely in the pursuit of self-improvement and self-education rather than delving into bitter bickering over politics or religion or whatever the cause of the day happens to be?

It's easy to optimize for the lowest common denominator.