"Because they wanted to" is the answer, I think. fwiw I feel much the same way and like the Original Sins in spite of them being turn-based but D2 is my true love of the series. Having said that, "in spite of" has still given me some very enjoyable games even if that isn't a part of it and I suck at more strategy-based combat!
It's certainly a never-ending debate, as the pinned topic in the BG3 forum demonstrates, and I think it's such a subjective preference that there's probably as little chance of anyone changing their mind as there is about e.g. their favourite colour.
I'd like Divinity 3 whenever it appears to be a successor to Divinity 2 both in terms of story and playing style/perspective, though that might be optimistic. There are other things that fit the bill even if they are a bit thin on the ground at the moment; but this year I found both Greedfall and The Outer Worlds enjoyable, both of which are that sort of "actually being there" third-person real-time game, and other recommendations include Dragon's Dogma and the often overlooked Kingdoms of Amalur: Reckoning.
