I think the idea is to conceal the confusing CC feature from those who don't understand it, since everyone involved in the email chain must see the box and not just the clever originator who threw the CCs in there. That is, Adam sends out an email with all the bells and whistles, but Barry has no idea what all those random abbreviations mean and they frighten him. Adam and Barry both mostly just want to know who's going to receive this thing, so Gmail hides the CCs but shows the name. I think there's the unspoken belief that CC/BCC is a complete misfeature and Google wants it to die silently for the sake of clean UI.

It might not be the right approach, but I see why they did it.