IMO Fallout 3 had it’s time frame shifted at some point in its development. I mean take Little Lamplight, it’d make sense if it were 5-10 years after the war, as would all the relatively pristine ruins everywhere. It’d also explain why getting fresh water was such a urgent priority… despite the wastelanders managing without for 200 years.
However, I’m guessing the “less then a decade after the war” didn’t square with the aesthetic and lore they wanted to do, so the time frame of the game shifted several centuries forward, leaving odd bits of “just after the war” lore and set pieces.