Grendel_Khan
Hero
There is a difference between interpersonal and inter- and intratribal conflict and the King of Kentucky with his motorcycle cavalry and slaves and what have you. Humans are pro-social but not necessarily conflict averse.
You can tell interesting stories in post-apocalypses born out of realistic stress-born human social structures, and stories demand conflict, which can very easily come from without or within.
Also, consider that what I'm describing as a sort ideal pro-social structure is born from (and potentiality only possible through) an apocalypse that has entirely dismantled the systems and structures of power responsible for the vast majority of human suffering and environmental degradation in the world. Consider that this makes me more pessimistic than you might think.
I'm probably overly focused these days on the climate collapse, and all of the attendant horrors already bearing down on us, so I have a hard time imagining an apocalypse that we recover from, rather than survive, in a diminished sense, and then just sorta watch get worse over time. The idea of bouncing back now seems about as likely to me as achieving FTL.
But fiction is fiction, right? And yes, in theory, the idea of a society reimagining itself for the better after a grand sweeping aside of past structures can be interesting to consider, in a Fifth Season or what-happens-after-Fight-Club way. But I'd propose that once you set a story long enough after an apocalypse that people have settled into any new sense of stability, with new structures, and the focus isn't still on fighting for survival against the odds and without with the weight of that apocalypse still shaping how people interact, maybe that's no longer a post-apocalyptic story. It's something else, maybe something very cool, but to me it feels like that would tip into other genres.