IGN did an E3 2021 interview with Nintendo Treehouse’s Bill Trinen and Nate Bihldorff, where they revealed why the official name for The Legend of Zelda: Breath of the Wild 2. The pair suggested that there is going to be a subtitle for the game, but they’re just not ready to reveal what it is yet.
Trinen said that “as for why we’re holding back on the name, you’ll just have to stay tuned because, obviously, Zelda names are kind of important. Those subtitles…they start to give little bits of hints about maybe what’s going to happen”. In the meantime, Trinen says that “[Breath of the Wild 2] is going to be shorthand and it’s natural for people to want to find a shorthand way to frame it. We’re still calling it the sequel to Breath of the Wild”.