The modern zombie emerged from an accident of entertainment industry economics. George Romero really like Richard Matheson's I Am Legend but couldn't afford to pay him to adapt the novel about hordes of marauding vampires. So, he changed the vampires from bloodsuckers to general-issue, undead cannibal "ghouls," and he made them not just pallid and sickly but rotten, closer to the European folkloric revenant from which the vampire had sprung two centuries earlier.
But in doing so, Romero demystified the undead, taking away the traditional association of resurrected corpses with magic, the occult, and even religious power. Earlier walking corpses had a moral and magical dimension. The ghost existed to right past wrong and to provide proof of the survival of the soul after death. Frankenstein's monster raised Promethean questions about the human desire to become god. The vampire had a fascinating glamor, not only of eternal life but also of the vast weight of history that sat heavily upon his or her immortal shoulders.
Count Dracula, especially, captured the mystical and occult dimension of the undead. Not only could he transform into mist and wolf, but he also attended the devil's school, the Scholomance. When he comes to Renfield at Dr. Seward's asylum, he speaks in the words of the Devil. In Dracula, the Count says: "All these lives will I give you, ay, and many more and greater, through countless ages, if you will fall down and worship me!" Compare Mark 4:9, where the Devil says to Jesus: "All these things will I give thee, if thou wilt fall down and worship me."
The best horror monsters combine terror with awe, existing in the dark place that leads toward a contemplation of the Burkean sublime. The Cthulhu Mythos is a perfect example of horror that builds toward transcendent experiences of the sublime. The terror of alien beings from the darkest cosmos serves a higher purpose, frightening the mind into an understanding of the vast, awesome universe surrounding us. But even traditional horror figures--the ghost, the vampire, the werewolf, the mummy (which is, really, a zombie with a brain), etc.--offer a taste of the sublime when set in their traditional Gothic framework of dark nights, crumbling architecture, a vast spaces.
The zombie is neither a magical figure, an occult figure, or a representative of the Burkean sublime. The zombie is no latter-day remainder of the mythological world view, no avatar of forgotten ages when other gods ruled the human mind. The zombie is a thoroughly modern monster, or rather not much of a monster at all. It is simply a body, reanimated, without mind. Even Victor Frankenstein would be unimpressed. His resurrected corpse read Milton. Absent all three traditional trappings of horror monsters--the Gothic, the occult, and the sublime--zombies are, like so many things in the modern world, hollow, plastic shells--poor simulacra of older, better monsters they have imperfectly replaced.