Mostly I see apocalyptic and survival fiction as just another way of creating a new fantasy world. You set the rules for this new world, somehow inspired by how (and when) the old world ended. The advantage over creating a totally new world is that you get to keep some elements familiar to the reader so that you don't have to build everything for them.
It also lets you keep the number of characters down
The first book I tried to write was something along these lines: a distant future sci-fi with an apocalyptic theme, I abandoned it when it started to feel like Red Dwarf without the humour. I still like some of the ideas I had then, I may even go back to it one day.
I enjoy reading such books when they're well done ... but that's all too rare.