Just look at the BG 3 opening cinematic and the current gameplay and you can see the discrepancy.
No game has ever looked like a cinematic trailer.
You seriously cannot compare BG1 and 2 to BG3 in terms of aesthetic. The resolution alone kills any comparison that you might try to make. I bet if they had today's tech 20+ years ago, BG1 and 2 would have been A LOT different, probably unrecognizable from what they are. They didn't have access to what Larian has access to.