If there's a constant stream of people wanting the game to give them more information on the setting, then I would take that as meaning the game has failed to give enough information. We also definitely don't need to know all those thousands of years of history either. Let me use Pathfinder as an example again. I've never played a game of Pathfinder. I've at least played a few sessions of D&D and read a bit of 5e setting stuff. But the only thing I know about the Pathfinder setting comes from context clues based on the similarities between D&D and Pathfinder. Yet neither of the Owlcat Pathfinder games left me feeling confused or unmoored from the setting the way that BG3 has.
Also, it's true that this is the third entry in a series, but it's a third entry that's coming about two decades after the last entry. If it were a book or even a movie I would fully agree that people should experience the first entries before coming to BG3, but this presses up against a rather unique problem that I think only games have. After a certain point, old games can get less enjoyable to play, as gaming conventions grow more streamlined, refinements are made and new quality of life inclusions become the norm. I tried playing the two Knights of the Old Republic games and I couldn't stick with them. Hell, the first Mass Effect game is one I don't enjoy revisiting because I find it more of a slog to go to. So for a lot of people new to Baldur's Gate, going back to play the first two games would be an unpleasant experience in the way going back and reading the first books in a series wouldn't be. Plus BG3 is wildly changing things from those first two games anyway, and it doesn't seem to be a direct sequal (maybe there will be a twist that reveals it actually is, we don't know yet) so it makes even more sense for BG3 to be more of an entrypoint for new players.
