Blame this.
Wildebeer
So, it turns out that the end of civilization may actually come down to the common wildebeest. Not nuclear holocaust, not solar flares, not a meteor strike, and not even [INSERT CURRENT TRENDY SOCIETAL ILL HERE]: the wildebeest. Who knew?
Although technically this may be a ‘genetic engineering’ sort of apocalypse: somebody as-yet-undiscovered was working on a better strain of fermenting yeast, it apparently got out of the lab, and managed to get established among the wildebeest population. Now about one percent of lactating wildebeests are giving fermented milk. Which tastes nasty until you can process it a little, but that’s not the problem. And no, the problem is not even that, if this problem continues, wildebeests will pretty much go extinct in the wild (booze and babies DO NOT MIX) in a generation now – well, OK, it’s a problem. It’s just not THE problem.
No, THE problem is that the genetically engineered yeast wasn’t supposed to find an animal host in the first place. So there’s no reason why it can’t jump from wildebeests to, say, other members of the Bovidae family. Which means sheep, goats, and cows… and that would be a real problem right there. Even if you don’t eat meat, losing humanity’s major sources of wool, leather, milk, other dairy products would result in bad things for the world economy. Sufficiently bad that there might be a war.
So far, there’s no sign that the yeast is jumping into other Bovidae. Believe me, people are looking. They’re also looking very hard at domestic pigs, on the grounds that while it’s comparatively difficult for infections and parasites to jump from bovine to human species, it’s dead easy for them to jump from porcine ones (also, avian ones: but fortunately chickens don’t give milk). In the meantime, there are any number of organizations both inside the government and outside of it who would be willing to hire a party of investigators who might be willing to act, ah, unconventionally, obsessively, and with a certain vigorous urgency towards the goal of finding the idiots who gengineered this yeast and getting them to cough up the design process. I wonder if that description would match anybody in your campaign’s adventuring party?