They have no eyes, but they can see, I tell you. No eyes, no! No eyes at all, but you can feel it looking at you, it stares through you, like looking through empty air, and you can feel it, raking your innards with their... "touch." The shiver of their senses combing your bowels through empty space...
— Dr. Maximillian Roivas, Eternal Darkness
Insects are a major pain in the ass for living humans, and in some cases, being able to swat away flies and having an immune system is the only thing keeping us from having our eyes and tongues eaten out by maggots. Zombies in any part of the world with a fly problem are going to be swarming with maggots in short order, meaning that most of their soft tissues will be infested, and their eyes will be very quickly useless.