They ask that questions also during student or work visa issuance - and even during the greencard (adjustment of status) and naturalization processes. They don't ask it every time you enter with these visas or statuses however.
But as a US citizen you will never be asked. And better yet if you are a dual citizen like me. Then you can travel on your other passport to the places the US finds to be undesirable.
I think green card and naturalization ask about travel in the last few years. But they don't ask about travel prior to that, and they don't ask about Iran specifically.
But as a US citizen you will never be asked. And better yet if you are a dual citizen like me. Then you can travel on your other passport to the places the US finds to be undesirable.