And it shouldn't be. Baldur's Gate 1 and 2 are amazing games that pioneered or popularized many things we've come to expect in modern RPGs, but they're also 20+ years old. If Bioware's Baldur's Gate was released today, it wouldn't be revolutionary. It would be an excellently made throwback to how RPGs used to be.
BG3 isn't made by the same studio, let alone the same people. Their admiration of what they're building upon is clear as a sunny day, though. So let this carry on the spirit of what was and be the foundation of something new.
Most likely? Nostalgia and familiarity. We'll probably never know if the decision to make it Baldur's Gate 3 was WotC/Hasbro's or Larian's.
There's precedent, though. Baldur's Gate: Dark Alliance had less of a connection to Bioware's BG than this one does.