Quote Originally Posted by snoopy13a View Post
They probably paid their taxes on time and wiping them out would be costly. Just because you can win a brutal war doesn't mean you should fight it. And likely, whomever replaced the ironmen as vassals wouldn't be as efficient in making money. So, tax revenue would go down.

In fact, Balon Greatjoy thought--wrongly, of course--that Robert would let him break away because the cost of subduing the islands is high. Balon knew that he couldn't win a war if Robert really wanted one; he just thought that Robert wouldn't think that a war would be worth it. What Balon didn't consider was that Robert had to show his other vassals that he was a strong king. So the war was about demonstrating political strength instead of economics.

Therefore, as long as the ironmen paid lipservice and taxes to the king, they were fine. It wasn't until they actually forced the king's hand that they had to be smacked down. That begs the question, of course, of why didn't Robert go Rains of Castamere on them when he had the chance? Outside the fact that Ned Stark and probably Jon Arryn wouldn't go along with it?
It's noted at least once that Robert was quite forgiving where others would not have been. Stupidly so from time to time.

Also keep in mind Tywin's comments to Joffrey that (and I'm paraphrasing here) if you don't help your vassals to stand back up once they've knelt before you, nobody will kneel before you again.