While using all the tropes of science-fiction, such as space ships, laser guns, robots, etc, Sci-fi does not concern itself with the big questions. In a Sci-fi story you will never find out how the spaceshp works, or why the aliens need human women/brains/dna, or how that laser pistol can hold enough charges to just keep shooting.
Basically Sci-fi is science-fiction with all the hard edges rubbed off so the kids don’t get hurt. It is fiction written to look like science-fiction without the writer having to know a thing about science. Sometimes it can be fun, with characters and events that can explore a speculative universe, without asking deep questions about how it came to be, but often it is just a little silliness with a scientific veneer.