Maybe it's just too subjective. When I put myself in the shoes of these people, the US can kill me at any time, with no warning, and nothing I can do about it. Being able to see it coming doesn't enter into the calculation. Also, I seriously doubt that you'd hear the plane that launched a supersonic Hellfire missile before you died.
It's not just about being able to see it coming, it's about being able to know when it's happening and when it's over. When you can either see it coming or hear/see it leaving, you at least get a feeling of relief after it's over. You can package a lot of your anxiety and fear into a discrete pocket of time. If you don't see it coming and don't know when it's over, you have to carry that fear and anxiety with you at all times.