Pay per ad incentives lead to rewarding viral content. And content that induces outrage is far more likely to go viral than pretty much anything else. Plus it goes viral before people do pesky things like fact checks. And the more of this that you have been exposed to, the more reasonable you find outrageous claims. Even if you know that the ones that you have seen were all wrong.
For an in depth treatment of the underlying issues, I highly recommend Trust Me, I’m Lying.