Car dealer Brad Sowers is spending money to prepare for the coming wave of new electric models from General Motors Co. He is installing charging stations, upgrading service bays and retraining staff at his St. Louis-area dealership to handle the technology-packed vehicles. But when he considers how many plug-in Chevy Bolts he sold last year—nine, out of the nearly 4,000 Chevrolets sold at his Missouri dealerships—it gives him pause. “The consumer in the middle of America just isn’t there yet,” when it comes to switching to electric vehicles, he said, citing the long distances many of his customers drive daily...