Makes sense to me.
Once chaos ensues (given catastrophic events), those in (US) cities and populated areas will die because they do not know how to survive on their own. Plus people will be killing people over food, supplies, riots, etc.
Alaska is the last frontier. Animals haven't been hunted and pushed out to near non-existence. Population is low and scattered about and not too many are tough enough nor smart enough to survive, let alone flourish.
Isn't Alaska, like located on this WORLD? So if the WORLD came to an end, Alaska would too. Unless of course it would detach and then float off into outer space before the world really did, end.