IMO this is caused by the ease of creating non-mainstream media sources with the internet. Before the internet there were only a handful of media sources (the "mainstream media") and since ~everone got ~all their news from them, society mostly agreed on the same news facts. This doesn't mean that the media of the time was always true and unbiased, just that people looked at it less critically. Now that there's alternative sources, people can find ones that better align with their beliefs, even if those sources and their beliefs are incorrect. Inevitably any source is going to be wrong some of the time, so evidence of mainstream media being wrong is treated as reasons not to trust them. As the underdog, alternative media gets a looser pass in most people's minds and are held to a lower standard. If people get sucked far enough into an echo chamber that they no longer regularly see opposing viewpoints then it's possible they don't criticise their sources at all as they look like they're always true.

The solution to this isn't fact checking, banning disinformation, or forcing unbiased media, because that creates an impossible standard that nobody will be able to reach all the time (which will cause the standard to degrade as exceptions are passed over). Instead, it's to cultivate media literacy: who's reporting this, why are they reporting this, why are they choosing these facts to highlight, why do they deemphasize facts reported by other sources, what's their long term bias and affiliation, and what are they trying to get you to believe. You need to apply those questions to every source and trust none of them implicitly, at least because nobody's perfect.