The attraction of all post-apocalyptic settings is the same: the absence of law. The modern world has liberated people in many ways, but in other ways the lives of human beings are more thoroughly regulated than at any other time in history, even in "free" countries. Everyone has identification cards and numbers, and everyone is surrounded by enforced regulations prohibiting them from doing things - even minor things - they want to do. No driving over a certain speed. No smoking. Cameras on every street corner. List your income on your tax form every year, and don't lie because we'll make your life miserable because it's what "we" voted for to support the greater good. No murdering the guy who abused your kid; you must allow "the system" to do its job.
Unfortunately the greater good always allows lesser evils to flourish; there are laws everywhere, but law is not the same as justice.
Now destroy civilization - or have it destroyed out from under you, so you have no guilt - and from the ashes you're free to make your own law and your own justice, free to judge what is good and what is evil, even free to decide who lives and who dies. But of course, other people are free too, which means you have to be able to defend yourself to make sure your ideals survive. It's a perfect justification for violent behavior, which is exciting and works well in stories and games.
Has anyone read "The Road" by Cormac McCarthy? Just wondering.