What the heck is “voice”? By this, do editors mean “style”? I do not think so. By voice, I think they mean not only a unique way of putting words together, but a unique sensibility, a distinctive way of looking at the world, an outlook that enriches an author’s oeuvre. They want to read an author who is like no other. An original. A standout. A voice.
Think about your favorite author’s voice. Can’t you recognize their writing immediately? Why? Because of how it sounds to you when you read it. Because you know they’re going to speak of certain things and do something that is trademark theirs.