Without a voice, there’s no presence in the story. It just sort of feels like the story is being relayed to us without the importance of character or narrative. Without a specific voice for your book, the characters can read a bit like a textbook. Readers want to see what the characters see, they want to know the story through the unique perspective of each character, not just a bland rehashing of the plot points. You’re writing a novel, after all, not a textbook!