I wonder if this is less of a direct cognitive bias, and actually a fully sensible approach.

I mean, let's face it: How many of us really have any meaningful control whatsoever over any Existential Risks? Even with man-made ones like global warming, any one individual's contribution is such a tiny drop in a colossal bucket that it hardly make a dent. It would take a massive concerted effort to adjust many of these issues, and most people are already over-committed in their lives -- they're not looking for another cause to gobble up their scant time and money.

So sure, if you already know a lot about a topic because you found it interesting, then take steps to feel like you're doing something: vote for candidates who seem like they're tackling the problem, opine on message boards and whatnot. However, for a person who doesn't know anything about the topic (and hence I'm willing to make the leap and say they probably don't find that topic interesting, or else they likely would have), doesn't it make sense that they would say "I'll let the specialists handle this one." ...And who do the "specialists" work for, when it comes to things like the environment, disease control, asteroid protection, etc? More often than not, the government.

What's the alternative? That each one of us runs off and studies every existential risk in our spare time, full-well knowing that our individual involvement will have approximately 0.0% impact upon how this existential threat impacts their lives? That, if anything, sounds like a cognitively flawed approach!