Byss is full of the dark side....and the dark side of the force clouds everything! so maybe they [rebels] dont even know it exists? other wise, its a pretty crummy deal b/c byss has a lot! of build spots
i took control of coruscant when the death star was just sitting at corleilla for the rest of the game then it didnt unlock so i went to corlag(i think) which was next to byss but it stil didnt unlock but i dont see why they didnt add it on i mean if they didnt know it exists then why not just remove it from the map?