Why did the Mentorians endure this, never quite trusted, isolated among aliens?

Raynor Three had said,Because I belong in space, because I'm never happy anywhere else. Bart looked out the viewport at the swirl and burn of the colors there. Now that he could never speak of the colors, it seemed he had never been so wholly and wistfully aware of them. They symbolized the thing he could never put into words.

So that everyone can have this. Not just the Lhari.

Rugel watched the Mentorians go, scowling. "I wish medic would find a way to keep them alive through warp," he said. "My Mentorian assistant could watch that frequency-shift as we got near the bottom of the arc, and I'll bet she couldseeit. They can see the changes in intensity faster than I can plot them on the photometer!"

Bart felt goosebumps break out on his skin. Rugel spoke as if the certain death of humans, Mentorians, was a fact. Didn't the Lhari themselves know it was a farce?Or was it?

Vorongil himself took the controls for the surge of Acceleration Two, which would take them past the Light Barrier. Bart, watching his instruments to exact position and time, saw the colors of each star shift strangely, moment by moment. The red stars seemed hard to see. The orange-yellow ones burned suddenly like flame; the green ones seemed golden, the blue ones almost green. Dimly, he remembered the old story of a "red shift" in the lights of approaching stars, but here he saw it pure, a sight no human eyes had ever seen. A sight thatnoeyes had seen, human or otherwise, for the Lhari could not see it....