This was news to me and it turns out that this is indeed the case: https://e-visa.ie/usa/news/iran-and-esta. They mention the 1st of March, 2011 as the cut off point, but I haven't been able to suss out why it's that date exactly. I'm guessing it has to do with the Arab Spring, but that is just conjecture. Hopefully someone can correct me if I am way off base.