At the point where he started writing Game of Thrones, he intentionally tried to make it as expansive and imaginative as possible, given he finally did not have on-screen budgets to worry about.
George R.R. Martin called it a challenge he didn’t originally think could be done, given his experience in 1985 and the years following in Hollywood.
He said that often the budgets for television meant that he had to cut down his ideas, making battle ideas singular fights between the hero and the villain and so on and so forth.