If u look at the special effects, u can understand why it took so long. You never know Will might have only decided he wanted a huge expensive video after switch was out, so therefore they have to get an idea, film it and then do all those effects.
I'd rather have the wait for something this big than something bland and boring and overlooked. Look what big videos and risk did for Micheal Jackson's career (in the 80's early 90's) never under-estimate what a music video can do.