Because, for better or worse, the sources of truth that normal people historically relied on for their barometer of what is true or not have been democratized by the internet.
We live in a world where a substantial number of people believe the earth is flat, that 5G cellular is a mind control scheme, that vaccines cause autism, that COVID-19 was created by a political party, that the concept of climate change is manufactured, or that major national crises are actually just actors being paid to further a political narrative.
Most of these ideas aren't new, but in decades past you might have heard about them from a conspiracy-therorist neighbor, a low profile website, or an alternative magazine with little reputation of its own.
Now, these ideas are spread on the exact same platforms as objectively truthful / scientifically sound media. Your Youtube conspiracy theory channel is right next to the BBC's videos. Your viral Facebook post could be from the New York Times, or it might be from a propaganda organization - or worse, an account that looks like a normal person but which was specifically created to spread misinformation that seems plausibly truthful.
Credibility is distributed and anyone can publish to a huge audience, which is wonderful sometimes, and othertimes deeply problematic, because the viewer often doesn't know enough to distinguish fact from fiction and can't trust the publisher at face value anymore.
Its uncharted territory. The cost to distribute is zero, and ideas spread far and wide - but that means that there are equally as many incredible sources on any given topic as credible ones, and telling the difference is hard, and sometimes not knowing the difference is dangerous. Dunning-Kruger writ large.