Why long-range weapons still led to visual-range combat in Vietnam

Why did US Air Force crews in the Vietnam War have to close to visual range despite having long-range weapons?

They had to identify enemy aircraft visually before engaging, which limited the practical use of their long-range advantage.

The exchange separates weapon reach from permission to engage. US Air Force aircraft could possess a long-range advantage while identification requirements still forced crews close enough to confirm the target visually. That constraint reduced the practical value of long-range weapons and shows how engagement rules can override technical capability.