Because they still do what they always do: Operate by rule of cool.
Rule of cool works awesomely for short stories.
It is utterly detrimental to big stories, more so when rule of cool makes it needed to change things on the fly.
Big stories in wow, never get written start to end in one go by one person, in stead there is a vague start and a vague end goal by various writers. It is comparible with the mess that became star wars eps 7-8-9.