I don’t think you can point at one proximate cause over any others without asking why Rome was vulnerable to that thing particularly.
My impression is that it was less common to outright deny reality and more common to blame at least the disasters and pandemics on those one found troublesome supposedly offending the gods.
The root-cause then must have been lack of democracy. Rome once had a democracy sort of right? But when the authoritarian emperors took over, you could say sayonara to "civil society".
Bad leadership is caused by people's inability to hold leaders accountable. In other words by lack of democracy.
Not really.
The Roman Republic had legislative assemblies and elected magistrates, but the deck was firmly stacked in favor of the aristocracy. Votes in the Centuriate assembly, which elected all senior magistrates, were heavily weighted by wealth. Originally the highest two classes, comprising those with at least 10,000 denarii in assets, controlled an outright majority of the votes. (1 denarius is on the order of 1 day's income for an unskilled laborer).
The weighting was somewhat reduced in the mid 3rd century, but Sulla's reforms around 80 BC reverted the change, and additionally stripped the more democratic plebeian and tribal assemblies of most of their powers.
The senate (ostensibly an advisory body, but by the middle republic actually a legislature) was never elected. During the early republic, senators were appointed by the consuls. Later, they were appointed either by the censors, or automatically upon election to a senior magistracy. In either case, appointment to the senate was for life.
Rome had Emperors for either 400 or 1500 years, depending on what you call Rome, while the Roman Republic lasted about 400 years at most, with a tiny percentage of the population having voting rights for most of it.
So blaming a lack of democracy is a huge stretch.