Because it has dragons - and dragons are stupid.
Any story that has dragons is immediately suspect. When you think of great stories - The Godfather, Casablanca, Bridge on the River Kwai (just to stick to movies) - none of them have dragons. And I'm pretty confident that they would not have been substantially better if they did. Even movies that you think could make good use of a dragon - Mad Max: Fury Road, Raiders of the Lost Ark, My Dinner with Andre, et al. - don’t really need any (except maybe for that last one). And even Crouching Tiger, Hidden Dragon doesn't actually have a dragon in it; and the title itself goes to great lengths to reassure the viewer that if by some mishap or oversight there were a dragon in this film it will remain hidden - you will not see it.
Dragons are for children’s stories. The only time I know of when a dragon shows up in an adult story (and by “an adult story” I mean a story for grown-ups, I don’t mean a pornographic story - though to judge by the tastes of Game of Thrones fans dragon-porn would be right up their alley*) is in Richard Wagner’s operas Das Rheingold and Siegfried. And even there the dragon doesn’t do much. Mostly he sits on a pile of gold and waits for the hero to come along and kill him. And traditionally that’s all dragons ever do - sit on piles of gold and wait for death. Now, I ask you, what kind of a life is that? They don't go out. They don’t have any friends. They don't buy anything. They live in a cave. They’re pathetic. No wonder they have anger and rage issues. In fact, if a dragon had cable TV and a bag of chips, he would probably be binge-watching Games of Thrones right now.
* But, of course, only if one of the dragons was tortured and killed in the process.