As far as I can tell it's mainly environmental. Isolationism is not a human survival instinctual characteristic. We are a herd species for safety and survival and tend to snap under long term isolation. That's why it's illegal to use for detainees under the Geneva Convention.
Conspiratorial thinking is a social product of the 1960's and later, exacerbated by cable TV and later the internet. Lower IQ people, in particular, are more drawn to conspiratorial thinking due to the "smart sounding logic" of the pseudo-intellectual conspiracy-mongers.
It's the sensationalism they're drawn to. Actual facts are pretty boring, but conspiracies make life sound like a Hollywood movie and people are bored with reality and inundated with information overload. So, like any addict, they seek "harder drugs" IE weirder conspiracies.
It's a cycle that leads to ingrained delusions that are as concrete in the individual psyche as those affected by religious cults and some will act out to defend those delusions. That's where the psychosis comes in. Think about how psychotic people get defending "muh Russia" lies
