Clearly you skipped over the Coleman Young Era of leadership in Detroit. Plagued by crime and rampant corruption, White flight started after a series of race riots in 1967, but continued through the 70s and 80s. Young succeeded in integrating the police department and reducing brutality complaints, but the murder rate never dipped below 50 per 100k residents and the city lost about half a million residents during his ~20 years of leadership.
Then of course you had later convicted crooks like Kwambe Kilpatrick run the city into bankruptcy. Auto companies, mainly GM and Chrysler, left, but that was only part of the problem. Years of fiscal mismanagement and crime deteriorated the city.