Don't forget 9/11 truthers. They were at least as popular as any modern-day form of crankery, and that was nearly twenty years ago now.
The difference is in how the disinformation is propagated. In the past media companies would self censure idiotic or untrue ideas to protect their reputations and while you could find information if you looked hard, the things would tend to spread slowly. Social media doesn’t profit from reputation but from engagement, and untruth is more engaging.