See this is why I think the TUTORIAL should be levels 1-3 and the midpoint of chapter 1 should be level 5. Levels 1 to 3 in D&D 5e are babbies first adventure, very little complexity and designed to get to know your characters.
the vast majority of all 5e games are levels 5 to 9, because that is where the "meat" of the experience is. The life or death battles, no easy resurrection, and the most well balanced combat
BG3 is going to be the introduction to 5e for a LOT of players. Larian probably does not want to overwhelm new players with the additional complexity and choices that you'd get if you were creating level 3 characters and needing to pick subclasses.
