Whole Foods Market, once the darling of the grocery industry, is facing a whole lot of problems. Poor shareholder performance threatens founder and CEO John Mackey’s position. New directors have been added to deter activist investors and improve relationships with major institutional investors. Some argue that for all its previous success, Whole Foods has not mastered Retail 101 and that is why it is failing. Perhaps – no retailer gets away with poor service and unnecessarily high prices these days. From my perch, however, the core issue facing Whole Foods is its business model. Organic and healthy was once a unique niche within the grocery industry, warranting a separate store. Now, fresh and organic are mainstream. Niches are alcoves — protected places. They exist in our natural world. In our economy, they’re specialized markets. By serving a narrower target market (Four Seasons versus…