My assumption is they thought they could kill the supreme leader and get Venezuela 2.0 where Iran's next leader ends up being a puppet to the US. I doubt they thought this war would be going on this long. They tested the waters with Iran in June 2025 and since Iran was still willing to negotiate even after that strike, I think the Trump admin assumed they could go a lot further and get even more favorable negotiations.

But it's true this hasn't been clearly communicated. I think, mainly, because it really wasn't well thought out.