 Why does Loy Chuk build an artificial environment for Ned?
A scream of brakes, the splash into icy waters, a long descent into alkaline depths ... His car hit the white-painted wooden rail sideways, crashed through, tumbled down a steep slope, struck a huge boulder, bounced up a little, and arced outward, falling as gracefully as a swan-diver toward the inky waters of the Pit, fifty feet beneath.... Movement was slower now, as he began to sink, trapped inside his wrecked car. The edges of that almost bottomless pool were caked with a rim of white—for the water, on which dead birds so often floated, was surcharged with alkali. Lacking qualities identifiable as human, the disturbance was still like the babble of a group of workmen who have discovered something remarkable. The icy breeze tore tiny puffs of dust from grotesque, angling drifts of soil, nearly waterless for eons. Loy Chuk had flown his geological expedition out from the far lowlands to the east, out from the city of Kar-Rah. He could think and dream and invent, and the civilization of his kind was already far beyond that of the ancient Twentieth Century. Loy Chuk and his fellow workers were gathered, tense and gleeful, around the things their digging had exposed to the daylight. The dry mud that had encased it like an airtight coffin, had by now been chipped away by the tiny investigators; but soiled clothing still clung to it, after perhaps a million years.
 He needs a habitat for Ned, so he can study Ned in a natural setting.
 He needs to keep Ned calm. If Ned believes himself to back in his own time, he will remain calm.  He realizes Ned is mentally unstable from the trauma of being brought back to life. He doesn't want Ned to commit suicide.  He needs a habitat for Ned until they can figure out time travel.  He needs a habitat for Ned, so he can study Ned in a natural setting.