A Song of Ice and Fire is not about kings. It’s about the people who surround, support and get stomped on by kings in quests for thrones and power. In older fantasy stories, the young kings are the heroes and lead characters, so George R.R. Martin subverted that by presenting his story through the perspective of everyone but the kings. The tale is now told by the rulers’ friends, mothers, children, wives, and the other people who usually become fringe characters. The only ruler with a point-of-view chapter is Daenerys, and she is not a Westerosi king.
Robert, Joffrey, Renly, Robb, Stannis, Balon- they don’t get to tell the story. They aren’t the heroes of the story. There may not be any, but if there are, it’s not them.