My best theory so far is that when it comes to telling people what they themselves need to do (as opposed to inactionable general fear), mainstream media narratives are based around telling audiences the easy answer that they want to hear - eg you don't have to do anything to prepare, and those that do are wrong. Obviously this has always been an ongoing quality (eg no need to oppose the Iraq war since it's just), but with a public health emergency it's front and center.