If people are worried about the setting not being appropriately desolate, struggling, etc, then consider natural disasters. I think the Fallout world is surprisingly absent of them. Earthquakes, floods, hurricanes, contagions, pest plagues/invasive species, could all stall out progress or claw it back. Human history is full of decline that didn't require any of those things specifically. Then of course there are unnatural disasters and, since this is Fallout we're talking about, there are plenty of options. So I don't really get the issue vis a vis progress.