In line with the Seagard discussion, I want to remind that since Aegon’s Conquest, the ironmen are strictly forbbiden to attack any westerosi ship. Adding to this, I suppose that in peace time most of the iron islands pirates sail mainly at the Narrow Sea, given that foreign merchants don’t seem to fear travel and anchor at Pyke, for example.

I think it’s a risk thing: in the last 300 years, there have been four episodes where the Ironborn have been actively attacking Westerosi ships/mainland:

• Dalton Greyjoy’s reaving during and after the Dance: ~3 years.
• Dagon Greyjoy’s reaving after the Great Spring Sickness: at least 3 years.
• Balon Greyjoy’s rebellion: 1 year.
• Ironborn invasions during War of Five Kings: 3 years so far.

So that’s 10 years (although could be more, because we don’t know when Dagon was brought down) out of 300, or 3.3% of the time.

The question is: is a 3.3% risk of piracy worth it?