Over the past two years, at least 16 major packaged-food and beverage chief executives have stepped down, according to a Wall Street Journal analysis. The departure of Campbell chief Denise Morrison earlier this month followed by CEO changes at General Mills Inc., Mondelez International Inc., Kellogg Co., Nestle USA, Hershey Co., J.M. Smucker Co., and Hostess. America’s food giants are shedding a generation of CEOs at a remarkable rate, the culmination of years of bleak sales in an industry that until recently had gone unshaken for half a century. The outgoing executives have contended with a new era of American eating and grocery shopping habits, shepherded in by millennials and the internet. Stalwart food brands no longer can consistently command higher prices from retailers, forcing management to focus on cost cuts. And as executives try to invest on change, investors want stronger profit margins. Investors said the CEO shuffle is a positive step for the industry, particularly when a new executive is brought in from outside. “There’s always a bit more intrigue when you have an external hire come into a company that’s been around for 100 years,” said Jacob Gamerman, senior research analyst at Neuberger Berman Group, which manages $299 billion of investor funds.