But fallout doesn't need to live from "MURICA FUCK YEAH" it would work great everywhere. And the 50s retro futuristic world building doesn't need to change at all.
GTA is little different, they just give you a island map and call shit similar to real world stuff, the muricaland part is basically just the Guns, and political statements during the story lines. Theoretically it would work without mentioning USA once, just take out the flags and you could say the game plays everywhere, organized crime is a thing in every country and you can get guns everywhere, especially if you are organized crime...
There is no point besides wanting to appeal to the usa centric consumers that think Europe doesn't have roads or that internet was invented in "murica"