If it’s hackneyed, pulp sci-fi types of movies, then @JLeslie‘s answer is most likely spot on. It’s easier to design a costume where the eyes actually are what the actor underneath sees through.
Thinking about creatures we know of, flies compound eyes are pretty weird looking. Their eyes are terrific at detecting motion, but pretty lousy at giving the fly a clear picture of what surrounds it and lays motionless. And even as odd as the fly eye appears, they do have two of them. There are a few outliers like the single eyed squid, and box jellies, which have 24 eyes around their bodies. Various sets the box jelly’s eyes are able to detect only certain wavelengths of radiation. One set of four is free to rotate in socket, always points up, and lets the jellyfish see the sky for navigation purposes. But in concert, the 24 eyes give the brainless stinging bastard of a squishy a pretty good picture of what’s around them.
But think about evolution on Earth, the exception proves the rule. Almost all creatures with any kind of advanced eye have 2 of them, set on opposite sides of their head. Grazing creatures (AKA prey) tend to have eyes on opposing sides of their skulls giving them a near 360 degree field of vision and thus helping them spot the motion of predators approaching no matter what angle they sneak in from. Predators, on the other hand, have two eyes in the front of their skulls, on opposite sides of their nose, giving them sharp binocular vision to see prey and calculate the distance to it. Good science fiction writers know this much science. They assume that life intelligent enough to travel through interstellar space would have gone through a predatory phase in its development. Having a really big brain requires more calories than grazing alone can easily provide.