From RTS to MMO to novels to film, Warcraft lore is rich in detail and scope. Thing is, the film is the latest piece of that particular series of events and as such, Hollywood gotta do what Hollywood does and figure out all the best ways to screw with the already well established lore (blog post) because fuck it, it's just a video game movie after all...
Source: Warcraft Movie Review - movie reviews Decker Shado