OR, it's because the Warcraft movie is severely flawed.
While I did enjoy the movie as a Warcraft fan, as a movie in of itself? It's lacking. Its pacing is rushed, there's a death of worldbuilding, many of its characters lack depth, it doesn't fully exploit its premise (it tries to juggle between moral ambuguiity, while also painting the orcs as monsters), etc.
I don't think Game of Thrones is a good comparison, since while both are high fantasy, that's about the only thing they have in common. Warcraft, regrettably, probably has more in common with stuff like Eragon.