Adding onto the other answers, it’s kind of like how counties and cities are renamed over the years. My city used to be called Port Arthur, now it’s Thunder Bay. Lots of places are like that. Pokémon may be a different world but surely culture and language developed over centuries, which is probably why the change.
I’d like to think the games will explain why they changed the name. War is cannon in Pokémon universe, so it’s possible something like that happened there, too.