[@Sigma] The world was conquered maybe ~150 years ago, and other life in the system discovered maybe 30-40 years ago. With that in mind, any currently living humans would not remember what it was like not to be ruled by the Empire. The human population on other worlds would be small, and mostly made up of refugees. It is entirely possible that people would attempt to leave, but such an act would be considered a crime. Aliens could make a fortune shipping people off the planet, but the Invigilator guns would make that one hell of a dangerous profession.