That's an easy question; a hard question is: Does it really take a formal "task force" to figure out the answer? Hardly. The behavior of Detroit residents scares-off grocery stores. Detroit city officials have for decades decided to create a regulatory and tax structure much less favorable than those in the surrounding suburbs. And of course too many Detroit residents have decided to behave in a much more criminal fashion than their contemporaries in the surrounding suburbs.
The article quotes a black Detroit council member as citing "racism" to explain why white-owned grocers shun Detroit. That's another reason for businesses to avoid Detroit: ignorant public scapegoating. Meanwhile, nothing prevents black millionaires from creating fabulous grocery stores in Detroit... nothing besides poor city management and residents generating some of the nation's worst crime statistics.