We know they're just optimizing for time spent on the site/app, as a proxy for the number of ads they show you and then get paid for.
But the thing that was supprising to me, as someone that remembers the world before the internet, is that anger is the thing that makes people stay on a site.
Before the internet came along, one would have thought that Truth would be the thing. Or funniness, or gossip, or even titalation and smut. Anger would have been quite far down on the list of 'addicting' things. But the proof is obvious, anger drives dollars.
There's no putting this knowledge away now that we know it.
The lesson only question is what are we going to do about it?