Heads dive into the sand on this issue.
Because it's so cosy and comfortable to have a reassuring 'aunty' making our fantasy world, filling it with cake shows, comedies, maaarvellous dramas and so on; and the top layer of Truth and Sincerity 'simply can't be questioned' or the whole thing comes tumbling down.
So mostly, people's response to being presented with blatant evidence of their beloved BBC and Guardian etc ... being used as tools to play down and cover up apartheid, our war crimes and so on - "the BBC is the most refined propaganda service in the world" John Pilger - is to brush it quickly away without engaging.
"Our cosy comfortable sofa is filled with cancer-inducing foam you say? And you have the evidence to prove it? Well that simply can't be true! I refuse to look. You must be one of those conspiracy theorists. Goodbye".
Equally, there's a section in 9-11 Architects and Engineers Explosive Evidence where psychologists explain about rejection of evidence that shatters emotional connection to a world view.