The game was done at launch. I played through the campaign the first month after it was released. I would have been happy with what was in the game a year ago

People bought the game and that enabled larian to keep working on it. So they got to polish and add in the stuff that had been left on the cutting room floor we'd have never otherwise seen due to that pesky reality of not being able to ship a finished product if the scope kept growing.

So now, a year after release, there's a whole DLC's worth of content in the game that we just get for free.