As the investigation deepened, more and more inconsistencies emerged.
People did not find the wreckage of Tos Civilization's enemy forces.
With each investigation going deeper, astronomical observation equipment at full power, most of the spaceship wreckage and robot wreckage found on the bases belonged to Tos Civilization itself.
"Either Tos Civilization was overwhelmingly crushed, with no power to fight back... or there really was a civil war."
Without clarity on the situation, that unknown risk always loomed, even possibly descending on The Kyushu at any second, making it impossible for everyone not to be cautious.
Fortunately, for now, "The Kyushu" was quite distant from that region, a full 10 hours away at the speed of light, so if any risk did arise, there should be time to respond. It's not like they could just run away without investigating anything...
