The "grim and gritty" is actually a bit of a retcon itself.
As was pointed out in Jimquisition's video on the show, the Fallout setting was originally a post apocalyptic setting where humanity was starting to claw its way back into civilization. Fallout 3 and 4 were originally the weirdos that stuck out for having a setting where it looks like the bombs were dropped only a few months or years ago rather than about two centuries and everyone was still living in squalid, burned out ruins.
I don't know if I completely agree with that. The "just bombed yesterday" aesthetics, sure, but it was still a grim and gritty universe in the first two games. Sure, there was a sign that a slow recovery was coming, but it was very much a wild "tribal/city state" environment rather than the large, relatively organized state that the NCR was by Fallout New Vegas. There's a reason those games were deliberately set away from the actual interior of the NCR.
(I also found out today that Shady Sands was supposed to have been destroyed in Van Buren)