It’s weird, but I suspect that Act 2 and Act 3 were swapped originally. It makes more sense to have Act 2 be where you go to Baldur’s Gate, learn more about your companions, resolve their personal stories, explore a large open map, and THEN move on to the big confrontation against the Absolute at the tower.

From a story perspective it’s really weird how you confront the Absolute and then go on to sort of aimlessly do all that other stuff in Baldur’s Gate. It makes more sense if the story acts are swapped, imo.