Well I think it's the story that Martin wants to tell. And part of that story includes shock, and has since day one. But for such an important character, I have to believe that the motivation was primarily telling a certain story in a certain way above all else. Either it's done so he can be revived, or done so that other characters can fill the gap he leaves, or done so that the story can pivot and really focus more heavily on others, or something else along those lines.