"Balder's Gate: Original Sin III" is what the Larian fanbase will demand so that's what we will likely get.
Who told you that? I am a fan of Divinity games, but i dont want BG 3 to be D:OS 3. These are completely different games, even if they are both RPG titles.
I guess that they didnt want to make D:OS 3 now, because they wanted to create something different. Thats why they decided to get the license and make a BG game.