Deflect threats to identities they hold, and roles they occupy
"Identity-protective cognition," a notion borrowed from Dan Kahan. Here's how Kahan and colleagues sum it up:
We propose that variance in risk perceptions -- across persons generally, and across race and gender in particular -- reflects a form of motivated cognition through which people seek to deflect threats to identities they hold, and roles they occupy, by virtue of contested cultural norms.
"Motivated cognition" refers to reasoning done in service of justifying an already held belief or goal. It helps explain why the CWM who know the most about climate science are the most likely to reject it; they learn about it in order to reject it. See Chris Mooney's great piece on that. Point being: when facts (or the implications of those facts) threaten people's social identities, they tend to dismiss the facts rather than the identity.
To all these reasons, I'd add "epistemic closure," the extraordinary way that the modern right has constructed a self-contained, hermetically sealed media environment in which conservatives can be protected from ever encountering a contrary view. It's an accelerant to all the tendencies described above.
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