To deliver on the expectations carried by the Baldur's Gate series name with an experience that is relateable to the series, and which resembles it rather than DOS2.
To be faithful to the brand and not use it as a cash-grab to promote the Divinity games, as Swen said he hopes "BG3" will do.
If Black Isle didn't think it right to call their cancelled 'Baldur's Gate 3' game Baldur's Gate 3 due to the differences it had with BG1 and BG2, despite that it would have still carried on the gameplay of BG1 and BG2, it's all the much more not right for Larian to call their D&D DOS formula game that bears no similarities with the Baldur's Gate series a "Baldur's Gate 3".
it's been a long time since i worked on The Black Hound, but i want to make clear (again) that i never had any intention of that game being called Baldur's Gate III or Baldur's Gate (whatever).
[Interplay] put that title on it after well over a year and a half of dev had been done.
they did it for contractual issues they had (they were only allowed to publish D&D games with baldur's gate or icewind dale in the title). i, and many others on the team, expressed concern over tacking the name onto a game that was made to be its own thing, not an IE/BG game.
the only connection it had was with IWD (maralie fiddlebender was a companion). it had no connection to BG at all.
in the end it didn't really matter, but i think it's important to note that the team's intention was never to use the BG name.