Sending things into space is obviously expensive as hell. One of the many, amny reasons why is the manufacturing process: everything that goes in or on a space vehicle has to be built in a clean environment, and there's more to it than just being generous with the bleach.
Tom Scott took a trip to Innovative Space Logistics, a Cubesat manufacturer based in the Netherlands. It has an ISO level-7 clean room, meaning it has one per cent of the particles you'd find in regular air. Cleanliness is achieved through double-walled rooms, plenty of filters, and a lot of special clothing.
Space hardware (and, for that matter, most sensitive consumer electronics) is assembled in clean rooms because one particle of dust on the wrong camera sensor can ruin a very expensive mission (or iPhone). But even more rigorous standards are applied for inter-planetary missions, in order to not accidentally bring life from Earth on a mission to find life on Mars.