 Based on the information in the text, why would Don choose to leave Superior?
Radio messages stated simply that Superior had seceded from Earth. But Don Cort, stranded on that rising town, was beginning to suspect that nothing was simple about Superior except its citizens. The state police converged on the former site of Superior from several directions. The object loomed out of a cloudbank at twelve thousand feet and Studley changed course to avoid it. A few minutes later he had relayed a message from Superior, formerly of Ohio, addressed to whom it might concern: It said that Superior had seceded from Earth. Don Cort had been dozing in what passed for the club car on the Buckeye Cannonball when the train braked to a stop. If the girl had given Don Cort more than that one glance, or if it had been a trained, all-encompassing glance, she would have seen a man in his mid-twenties—about her age—lean, tall and straight-shouldered, with once-blond hair now verging on dark brown, a face neither handsome nor ugly, and a habit of drawing the inside of his left cheek between his teeth and nibbling at it thoughtfully. Don hesitated, shrugged at the redhead, said, "Excuse me," and followed the conductor. Don made his way up to the locomotive and found a bigger knot of people gathered in front of the cowcatcher. Don Cort and the fireman walked cautiously toward the edge while the professor ambled ahead with the familiarity of one who had been there before.
 He had to deliver the handcuffed briefcase.
 He had to deliver the handcuffed briefcase.  He had a family to return to that would be expecting him at home.  He feared the future of Superior.  His wife would not appreciate him spending time with Alis.