It isn't the magnitude of evil but the remoteness - we know about life in the United States. We don't know many details about a secretive repressive nation. There are also flaws about 'requiring far too many people to keep a secret' and some major 'game theory'. Now it is a matter of fact that he was involved with sex trafficking and corruption but there were plenty of reasons to doubt.
The story hit upon a number of other discredited conspiracy tropes and archetypes. A network of child sex traffickers resembles too much 'orderly world' conspiracy theorist family. Where there is some vast conspiracy to blame for everything wrong with the world but there is at least someone behind it and some concrete goal to 'fix it'. As opposed to a chaotic real world where there is nothing that can be done about it - sometimes some nut-job decides to do something really scary like kill the president or shoot up schools.
Not to mention the anti-semetic tropes hit upon by it when there was a simpler explanation for his contact with high level people - he was rich. Being a donor would have explained it far easier than a sex trafficking conspiracy before concrete evidence.
Frankly the 'believers' of the story did more to make less believable than any amount of spin-doctors with things like drawing tenuous connections to anyone who ever met the guy being a pedophile.