Ovinomancer
No flips for you!
To start, I don't think it's an excuse -- there's not much to excuse, just a poorly presented premise. I happen to think the premise is important -- it's one of the reasons I ended up finding SKT lackluster as written -- it has a cool premise but never delivers on it. Frostmaiden, as I've skimmed and read in synopses, has both this part of the premise that's very shaky AND takes so many twists and turns it doesn't really deliver on it, either. Endless winter should be terrifying, and having survived two solid years of it already and things are starting to get bad doesn't deliver that at all.Every 'excuse' that's been used in this thread is, in the very least, implied in the adventure. I suspect it's probably (at least partly) by design that there isn't "one way" for everyone to have survived up until now. Perkins especially seems to like to leave lingering notes for DMs to riff on.
I think nearly everyone agrees that "two years; no light; minus fifty" is too much. Then again, the book says that people, plants, and animals are struggling, but still surviving, so I don't think that it's too much to assume that one shouldn't take that premise too strictly (unless they really want to, for whatever reason).