My suspicion is that when recipients see the cc with a name they don't know, they're suddenly in the position of making a first impression on someone that don't know yet, but will probably be working with in the future.
Another possible (related) thought -- here's an assistant who will be taking over some of these conversations, and thus they're probably talking about me (...so if I don't reply now, that's what they'll be discussing).
People care what others think of them; these people already know the original sender and have a stable relationship they don't feel will be threatened by a slow response (which easily slips into no response); but this adds a new person into the mix.
My suspicion is that when recipients see the cc with a name they don't know, they're suddenly in the position of making a first impression on someone that don't know yet, but will probably be working with in the future.
Another possible (related) thought -- here's an assistant who will be taking over some of these conversations, and thus they're probably talking about me (...so if I don't reply now, that's what they'll be discussing).
People care what others think of them; these people already know the original sender and have a stable relationship they don't feel will be threatened by a slow response (which easily slips into no response); but this adds a new person into the mix.