And yet the graphics are obviously better and more immersive than BG 1 and 2. Of course they build their technology from their previous games, but it doesn't change the fact that most other CCRPGs are less immersive for most gamers. I am pretty confident that high fidelity 3D graphics attract more gamers than isometric 2D, no matter if these look like the studios previous game.
TBF, BG3 is still at its core a top-down "feels-like-an-isometric-camera" game, this is still the best solution for managing a whole party of characters, especially in combat (unlike Witcher3 for instance, which has a traditional 3rd-person camera - but has no party to manage).