I produced a video about 8 years ago for Wayne County (the county Detroit is in) that was basically going to be an infomercial soliciting suburbanites to donate money to fund the destruction of urban decay. It focused mostly on residential neighborhoods that the county had to assume (from the city), and had not the budget to demolish.
The flight of the affluent to the 'burbs after WWII and especially in the 60's and 70's caused an erosion of the tax base, and I just cannot imagine trying to administer a place like that.
My dad tells me that most of the ruins that populate Detroit to this day are actually remnants of the '67 riots which burned approximately 1/4 of the city. 40 some-odd years later and they still cannot afford to tear them down properly.