Re: A Cleanroom?!
All satellites are assembled in a clean room.
It's perfectly normal for all satellites to have optical elements. The satellite needs to point in the right direction. To do that, the satellite first needs to know what direction it is currently pointing in. And there's (effectively) no gravity, so you can't just figure out what is "down".
So satellites have sun sensors for coarse attitude sensing, and star tracker(s) for precise sensing. Those are not going to take any usable pictures of Earth. The sun sensor just says " the brightest thing is that way". The star tracker is designed to take photos of dim stars, Earth is too bright for the camera and lens used.
The rocket will have optical sensors for those things too.
No-one wants random dirt to evaporate in the vacuum and then condense on those sensors.
Even ignoring the optical elements, no-one wants dirt clogging up the release mechanism between the satellite and the rocket. Or the release mechanism that deploys the solar panels and radio antennas. Or the thruster used to position the satellite. Or the reaction wheels sometimes used to turn the satellite.