Why though? I have provided evidence that this could be done without a negative effect on the game. Why can't the game evolve into something more?
Actually, I don't think the current state of the game is what was intended by the developers. Radiant Story was supposed to make the game much more dynamic than it is. I don't think they were able to make it work right.
In the lead up to the game's release, Radiant Story was talked up big time. We were told that it would automatically have the game react to the player's actions. If we killed an important quest giver, the game would replace that character with someone else that could complete the quest ... stuff like that. We would be able to ruin local economies. Family members of murder victims might come hunting us down, etc. Clearly, that's not how the game actually works.
To me the current state of the game measured against promoted features tells me that they simply couldn't get Radiant Story to work reliably enough in the long term and had to turn large segments of it off. Having done so, they had to 'patch up' the voids left by the absence of Radiant Story, doing things like making far too many NPCs essential because the system they had in place to deal with their deaths was no longer functional.
I even read somewhere that they had relied heavily on Radiant Story for quests, but came to realize that it didn't tell good stories, so they had to change course and create more traditional quests. This is probably why the guild quest lines were so short, because they lost too much time trying to develop a system that they never could get to work.
I'm actually optimistic about the quality of DLC, because I suspect they will stick with what they know works from the start in development.