Maybe I'm wrong but as I see it, it's...
The developers who did BG1 and 2 just think about developing a good game, fun, based on D&D but with all the advantages a video game could brought.
It looks like the developers who are doing BG3 are focus on creating a game which will be a D&D game and a DoS style game, forgetting the advantages a video game can brought.
I know my english is terrible (more it's very late here) but I hope you will get my point.
When looking for developping an amazing game thx to the knowledge of D&D seems like a good idea.
Overthinking and trying to give life to a pure copy/past of pen and paper D&D in a video game may be a bad idea.
One exemple (a good one, cause a major disagreement) :
The original devs may have think "hey guys ! Imagine, we are going to do a game with real fights ! It's gonna be soooo cool ! Finally we are going to be able to experience fights in reality time !"
The actual devs may be thinking "hey guys. We have to re-do it as a pen and paper game. So, forget about real time. we must do it turn-based cause this is how it is and who give a fuck if a computer is able to give life to some freaking amazing big real time battles ?"
Of course, it's just my opinion.