YEAH that story kinda set the bar for me with post apocalyptic yaoi but i mean it’s only 9 chapters or so — maybe that’s why the author/artist had more time?
They do explain it, with the Dead Man's Switch lecture - their world was trying to make sure that the "bad" ending wasn't being achieved. It's the same premise as Groundhog's Day or Happy Death Day - we don't get any explanation of why it happens, just that there is some situation that needs to happen or for them to solve the time loop to get out of it.
Plus the title is kind of clever that way - Dead Man's Switch is both about zombies (as in, dead people "switching" to being undead) and a failsafe for when something bad happens.
It would be nice if there were some side stories and explanations about the time loops and their life going forward, like in "A Room Without a Window". That one has quite a few side stories showing how they are doing after all the chaos and zombies
(づ￣ ³￣)づ