According to Houser, there is too much "Americanism" in GTA's DNA for the game to work in another country. The London episode on PS1 was more of an experiment.
During the Summer Game Fest, representatives from Bethesda Game Studios said that Fallout is "likely" to never leave the United States. This is because the franchise relies on events that take place specifically in America and its post-war, atomic world.
Dan Houser also noted on Lex Friedman's podcast:
«We did a small GTA London 26 years ago for PS1. It was nice and fun. But there is too much Americanism in and it would be difficult to move it to London or anywhere else. You need guns, big characters. The game is entirely about the USA, possibly from an outsider's perspective».
Historically, GTA has moved players from fictional Miami to Los Angeles, from New York to a brief foray into North Dakota. A similar situation with Fallout: Todd Howard confirmed in 2024 that the franchise will not leave the United States, leaving a mystery about what is happening in other countries.