It simply has goals that are different from history documentaries. It thrives in fantasy stereotypes whose intersection with history is flimsy on purpose; these are stories about dragons and magic, after all. This is not Braveheart being hilariously erroneous while at the same time purporting to be about real history, only "slightly" exaggerated: Game of Thrones completely disregards the real world, and because this is on purpose, I think criticisms from "realism" are unwarranted -- unless being done just for fun, like this author seems to do [1].
Besides, it's a sliding scale: Game of Thrones, by real world standards, is probably more realistic in its unreality than, say, Lord of the Rings. Neither is wrong to be unrealistic, being more parables or entertainment than actual history.
Of all the criticisms to be made of A Game of Thrones as literature, I think "being shallow" is not one of them.
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[1] https://acoup.blog/2019/05/28/new-acquisitions-not-how-it-wa...
> "Finally, before we dive in, two final caveats. First, this is not a criticism of George R.R. Martin’s world-building. There is, after all, no reason why his fantasy world needs to be true to the European Middle Ages (we’ll talk about known/possible historical inspirations as they come up). I do not think Martin set out to design a sneaky medieval culture lecture in fantasy novel form, so he cannot be faulted for failing to do what he never attempted."