Maybe the fans of the old games are not the game target audience anymore for reasons known by the Sales department. I mean, they are using D&D5e Assets, they are advertising modules of WOTC together (Descent into Avernus, etc), they are doing interviews together with WOTC CEOs, working with D&D5e creators, using the ruleset and the setting...
But I dont´remember them referencing the old BG games in any interview unless asked first (In one interview even Sven Vincke and Mike Merle didn´t remember the canon ending of the baalspawn crises), they didn´t make videos of "Sven Vinke playing the old bg games", didnt´hire any of the original game screenwriters, musicians,... didn´t use images of the old games and characters to advertise the game (Owlcat, for example, included two of the iconic characters of Pathfinder in the videogames, Amiri and Seelah),... didn´t take people from Black isle into the game-cons,... and they do none of the things that the PR department use to do to rally the old game fans.
These are all recognisable terms that could have been used in a game title to give the necessary marketing flavour to a new game not directly related to the original story. There was no need to actually call it BG3, and in doing so they were wilfully appealing to the goodwill associated with the original games.
It may well be true that they have made no other hires or references whatever to the original games, but in choosing a name that screams sequel, Larian made a rod for their own back.
Personally, I don't care if it is a sequel to the original story, and I don't have any desire to retain any of the implementation details of the original games, but at present it is really not clear what BG3 actually is, which leaves it open to criticism based on assumptions.
It remains possible that there are deep and satisfying links to the original story arc that might justify the sequal tag in terms of story-telling. And it remains possible that the game will be a superior single-person, party-based role-playing experience in the Baldur's Gate region that might justify the sequal tag in game-play terms.
But the evidence for either seems thin at present.