My opinion is this is due to a reduced level of trust that we place in either each other or large companies/organisations. It is known among the business industry that trust is lower than it was historically. Companies and people are increasingly seeming to engage in shadier and shadier practices, or we're becoming more aware of it. This erodes the level of trust we place in each other, research bodies, governments, policing and science etc.

In addition, where someone with an extremist view might be considered an outgroup, historically their views might have been suppressed among their peers or shutdown. Now they can engage online with thousands if not millions of other people who believe in the same out group ideas, potentially strengthening their view point.

One of the interesting psychological discussions is around people with extremist views such as flat earthers. These individuals are often minorities or outcasts of society and as such, many of those with extremist views form bonds with like minded people and their relationships and well-being are tied to those relationships. What this means is that not only are they less likely to respond pragmatically to opposing viewpoints, but that they would struggle to actually change their ways given that their relationships are tied with this belief. And if they were to believe differently, they would have to say goodbye to those bonds.