https://www.gamespot.com/articles/bethesda-is-less-likely-to-allow-an-outside-studio/1100-6460518/

2010's Fallout: New Vegas was developed by Obsidian Entertainment, not by Bethesda Game Studios itself. The game was generally well-liked, with GameSpot praising its big, detailed open world and quests filled with personality. While Obsidian has said it would like to make another Fallout game someday, it sounds like that won't happen. Bethesda boss Todd Howard said in a new interview that the company would rather develop big games internally.

He told The Guardian that he isn't ready to say definitively that a Fallout game from an outside studio won't ever happen again--but don't count on it.