It’s called Dark Matter. C’mon, what’s more likely, 85% of the universe is completely unobservable by chance? Or by design?

Any post-scarcity civilization that advances past Prime Directive territory just quantum-shifts half a dimension to the left so they can all hang out together without bothering anyone else.

Aliens don’t judge you, though. No judgemental species can collaborate long enough to go Dark, you either evolve past those primitive instincts or self-destruct.