I have only anecdata for this, but I have a strong suspicion that people just don't think about things on social media the same way they do physical interactions.
If someone standing outside the grocery store hands you a flyer that claims the government can control the weather and they're sending you hurricanes on purpose, you'd dismiss them as insane and continue on your way. When your high school buddy Denise posts it on Facebook, though, you're more likely to believe it. Even if you'd think Denise would be crazy if she went out and handed out flyers at the grocery store.
It's like most of us have a built-in crazy filter that works fine for in-person interactions, but it breaks down when that exact same interactions happens online.
I'm not so sure about this explanation; people believed in conspiracy theories in the past. Witch-hunts for example are fundamentally not that different from Q-Anon and all of that bollocks: "mysterious dark forces do evil stuff when we're not looking".
The whole "they're abusing our children" is also a trope that goes back a long time, most recently during the 80s with the whole "Satanic Ritual Abuse" stuff. That was much worse, because innocent people's lives were complete wrecked over what was complete bollocks. Pizzagate is near-identical, with s/daycare/pizzahut/.
More examples can be found throughout history – they're typically not called "conspiracy theories", but often they're not that different at its core.
I think what social media has done is allowing people to reach a wider audience. That person outside the grocery store reaches what, maybe a few hundred people with several hours of work? On the internet you can reach about 1.5 billion English speaking people with a minute of work. And that person outside the grocery store has no real way to organise a meaningful community, even if they do manage to gain 2 or 3 acolytes. On the internet you just create a Facebook group, or reddit sub, or whatever.
And all of that is including only the "crazy people". Add bad faith actors to the mix spreading misinformation simply to cause chaos and things quickly become well fucked.
This is why I never believe a tweet that I can’t confirm myself. I only pay attention to sciencey/CS people on twitter. Talking heads and political sources there are always nearly extremely biased and most are flat out untruthful.
If someone standing outside the grocery store hands you a flyer that claims the government can control the weather and they're sending you hurricanes on purpose, you'd dismiss them as insane and continue on your way. When your high school buddy Denise posts it on Facebook, though, you're more likely to believe it. Even if you'd think Denise would be crazy if she went out and handed out flyers at the grocery store.
It's like most of us have a built-in crazy filter that works fine for in-person interactions, but it breaks down when that exact same interactions happens online.