The reason it works so well for DAO, is the fact that Bioware created their combat and skill system from the ground up, for RTwP.
Translating tabletop DnD rules of any edition just doesn't work well since in every version, there are mechanics that rely on a TB system to be implemented properly.
Yup creating a system specifically for RtwP definitely helped. But it's not impossible to create such a system for D&D, depending on the how strictly you care about the implementation. The RtwP systems work pretty well for P:Km and BG1&2
Yup, this is how I see it. I like D&D well enough, mainly because it has been around for a very long time and it is what introduced me to the genre of RPG games. But I am not wedded to D&D rules and mechanics in the least bit (Dragon Age and PoE mechanics are both WAY superior to D&D for me), and so if a developer were to create a game that is "based on D&D rules," it is perfectly reasonable from my standpoint for them to also say: Hey, we want to use RTwP in our game, and as such we are going to be changing or leaving out anything in D&D rules that cannot be implemented well in RTwP. Not saying this for BG3; just making a general point.