DETROIT—U.S. new vehicle sales rebounded slightly last year from 2020’s dismal numbers, but forecasters expect them to be more than 2 million below the years before the coronavirus pandemic. The reason? Although there are plenty of customers who want to buy new vehicles at hefty prices, there still aren’t enough computer chips available for the industry to fully crank up its factories. So supplies are short, prices are high, and many customers can’t get what they want. “Demand is not off at all,” said Michelle Krebs, executive analyst for Cox Automotive. “What is off is sales, because the inventory doesn’t exist.” Cox expects 2021 sales to be 14.9 million vehicles, up 2.5 percent from 2020, the year the pandemic hit the U.S. and forced the industry to shut down for eight weeks. But over the five years before the pandemic, sales averaged 17.3 million. Among the hardest hit by the …