Interesting, that’s rare up here. I’ve never encountered it just across the stateline in Washington (or visiting northern Idaho, for that matter). Generally bothered only by a few indoor flies.
I agree. I lived in Idaho for about 45 years before moving and spent most of my summers camping and I never saw anything close to that experience.
Even when hunting in the early season when it's still warm, I never had that many blowflies show up to fresh offal piles. Initially, I thought maybe we set up camp by some attractant but it was pretty much the same everywhere we went on part of the Coeur d'Alene River.