And the huge and opaque organization required to make the modern world work provides a fertile ground for imaginations to run wild.
I think at this point it's so deeply ingrained that we're all somewhat susceptible to it.
Jones spread equally ridiculous theories about school shootings.
And the first thing fringe folks tell you is, "you are right, you are smart, you are clever. You've seen that they are covering up the truth, and you are wise to start questioning everything."
Once you get isolated by a bunch of media that tells you how impressive you are and tells you that anyone questioning you is trying to hold you back, you get separated from those who care about you. Once your loved ones give up on you, you turn to forums and chat groups of others in similar situations. They also tell you that you are smart and clever.
It's a classic abuser playbook, and unfortunately it's really really hard to unwind after a certain point. And we value freedom of speech too much to cut off the early on-ramps to this path. But we don't fund the education or the high quality information sources enough to help provide alternatives or defenses.
I suppose the most concise answer is really just "ideology".
In this case, I would imagine it’s: school shooting happens. Politicians use it to push for gun control. Therefore politicians made it happen, so they could use it.
Both sides of the political aisle do this, and plenty of people do it about less political things as well. It’s honestly my least favorite part of the public discourse right now.