I'm not quite sure what it is about toilet paper to be honest. But me specifically, I'm actually not surprised as it's been a conceit that I've been aware of for almost a decade. I'm not sure how much of the general populace is aware of Supernatural the TV show, but I've pretty much watched it from Season 1 through Season 12. One of the things that sticks out to me is an episode where one of the characters travels into the future where something like the apocalypse has taken place and demons and humans are fighting for control of the world.
In the future, one of the characters tells the time traveler to hoard toilet paper when he goes back to the past like it's gold:
It turns out, the guy telling him to hoard the toilet paper? He's God. Literally.
Anyway, the scene always struck me as something clever along the lines of "Oh, yeah, I've considered that I'd need food, water and medicine in an apocalypse, but toilet paper's pretty important now that I think about it."
This was the first place that I encountered the idea of TP in an apocalypse. Is it possible the idea originated here?