Is that a joke? Pathfinder: Kingmaker has a good rule set, which did not come from the studio. It came from decades of development over the life of D&D, leading to d20, 3.5, and then Pathfinder.
Is there anything else good about it? Certainly not the engine. Maybe the game gets better -- I can't tell, because it's unplayable now.
Nothing has stopped Obsidian from using Pathfinder, it's been out for a while now. While there's still bugs, Owlcat has pretty much figured out RTwP gameplay things that Obsidian never could, stuff like AI (especially companion AI), the overmap, resting, inventory management, an intuitive UI. You know stuff that actually makes people want to play the game.