I can't explain it either, but maybe prophesies of impending collapse are a bit premature. The world has never been particularly rational, even in places that have near 100% literacy. Just look at the number of people who believe in astrology or homeopathy, not to mention that one guy who created the Earth and its inhabitants some 4000 years ago, in six days no less.
Fair enough. But I'll just say that I feel like I've seen a pronounced change in my lifetime, and more pointedly in the last 5-10 years, that I find acutely disturbing, even compared against that "background rate".
And maybe the answer really is as simple as "social media". Which I find to be a sad idea, as the potential of social media act as a force for good still exists and is something I've always been particularly appreciative of.
For myself, the last 5 years have been a qualitative change. I don't think the unreasonableness of the world has increased that much per se, but since COVID it has started to intrude into my life in ways that it didn't before. Social media, or abuse thereof, seems a likely culprit, but there's probably more to it. In any case, I mostly agree with you, despite my previous comment.