I don’t think it’s debatable that they are, when you’re talking about the base. On almost any subject, they seem divorced from reality (climate science, election fraud, QAnon conspiracy theories, etc.). Thom Hartmann (profile here), a liberal talk show host, has theories; read them here. To briefly summarize,
Reason #1: Conservatives are attracted to authority figures and “father knows best” thinking, i.e., they’re less inclined to think for themselves.
Reason #2: There’s more conservative than liberal misinformation in circulation.
Reason #3: Conservative emphasis on individual freedom over social welfare makes them vulnerable to corporate sales pitches.
Reason #4: “Guardrails” against manipulation have been removed.
Reason #5: They lack critical thinking and media literacy skills.
But keep in mind the GOP is led, and the lies are spread, by smart people who know better than to believe the stuff they say. So there’s an ethical component to this that mustn’t be overlooked. For example, Mitch McConnell is obviously very smart, but he’s also ruthless. A quintessential Machiavellian politician. The fact the GOP intellectual elite are willing to subordinate truth, ethics, and decency to political expediency automatically puts Democrats at a disadvantage, because the latter won’t cross lines that Republicans are willing to cross. If Democrats addressed that by becoming more like Republicans, would that really solve anything? Then we’d have two irresponsible parties instead of just one.