> "BG3" on the otherhand innovates on Divinity: Original Sin 2 instead and then slaps a Baldur's Gate paint on the result.
Do you think that the setting, themes, story, and RPG rules are just 'paint'? Is the Infinity Engine so much more important than the Forgotten Realms?
> I also don't see why games should be inherently different from other media in this respect.
Because games aren't media: games are media generators. The same game can be a tragedy to one player and a comedy to another. So you can have two different kinds of follow-ups: ones that simply generate more media in the same way ( = expansion), or ones that improve on how the media is generate ( = sequel). The distinction doesn't make sense for fixed media like novels or films.
Note that I'm not talking about video games in particular, it applies to any kind of game. If I publish a book that adds a new secret level to the crypt of Acererak in the same style as the original, it's an expansion. If I publish a story about a different crypt that feels connected to the original but with its own unique design choices, that's when I can call it Tomb of Horrors 2.