Express Inc. and its subsidiary Bonobos, which filed Chapter 11 bankruptcy in April, have been purchased by a consortium headed by mall developer Simon Property Group. This is Simon’s latest retail rescue mission. Over the past five years, the developer has stepped in to save struggling chains like J.C. Penney, Brooks Brothers, Aeropostale, Forever 21 and Lucky Brand. Why does Simon keep investing in these struggling retailers? Because no one likes to shop at a half-empty mall. The developer has calculated that it’s better to keep some of its faltering tenants in business than to let them fail and end up with a bunch of vacant storefronts. This new plan means that Express will likely keep its doors open at Westfield Montgomery mall. But it comes too late to save Bonobos, which closed last week.