CHICAGO—The sprawling McCormick Place became America's convention headquarters when it opened here 50 years ago, hosting buyers and sellers of products from candy bars to windmill turbines. But in recent months, a gradual drop-off in business here has turned into a rout as a string of high-profile shows have pulled out. With the recession cramping convention business across the U.S., exhibitors say Chicago's high costs and complex work rules make other venues more attractive. Chicago's Metropolitan Pier and Exposition Authority, which runs McCormick, had an operating loss of $3.6 million in the fiscal year ended last June and expects to...