Comment by Ajedi32

They actively amplified any content that got high engagement, not ragebait specifically. That's why you see this trend across nearly all social media, not just Facebook. There's a strong financial incentive to get people to engage with your service, and amplifying the content that is already getting the most engagement is a simple way to do that.

You could blame this on advertising, but I think even if Facebook were a paid service (ignoring for a minute that that would have killed any chance it had of being successful in the first place) there'd still be an incentive to prioritize content that people's revealed preferences indicate they want to see more of.

Countering this natural human tendency requires a significant, thoughtful, concerted effort on the part of everyone involved.