The Sector is decaying. Dying, even. There aren't a whole lot of people around, sure, but there also isn't a whole lot of new places to move if the population *was* expanding. There are precious few inhabited places where you can breath "free" air. The technology to improve anything substantially belongs to a lost era. This is a perfect recipe for people to be treated as disposable.
I dunno, I've found some pretty nice places whilst exploring across my various games - a lot of them once even having
been inhabited, just abandoned or decivilized. But the Powers of the Sector are too busy squabbling to send colony expeditions of their own it seems - perhaps they fear that launching and supporting such an operation would require enough resources to weaken them and leave them vulnerable to an attack from their neighbours? Or that their new colonies would simply be jumped on by their opponents to avoid anyone gaining the upper hand?
Why don't they do the same to the player colonies? One, because you're an independent operator they may not be spying on constantly (so, by the time they know you're established, it's too late for them to intervene) and two, because it would just suck from a gameplay perspective to have all these neat colony establishment/management systems and then basically say to the player "lol, lmao, you thought you could use these? no. you sweet summer child. you absolute fool. go back to scrounging in the dirt just to survive." Might as well not even let players set up colonies at all if it could be that kind of noob trap that gets them gameover'd - or worse, just kills their interest in the game and causes them to not recommend it to their friends.
In reality I think it's best to realize that it's one of those things that is there for rule of cool and gameplay alike. There need to be
some consequences to fighter usage, otherwise they risk becoming too powerful compared to conventional weapons. It also allows there to be a handful of unmanned aerospace vehicles (like Wasps, and [REDACTED] fighters) that stand out more in this context and provide a glimpse at
What Could Be, for better or worse.