Why are certain areas in the United States so badly neglected by the government?

I know all big cities have their fair share of problems. But I am interested in why certain areas of the United States (i.e. Detroit, The Bronx, etc.) are so neglected in particular. I noticed something very interesting while I was in Detroit for a DUB show. There was a house that was abandoned and burnt down not far from a restaurant we were in. But that burnt down house had 2 brand new Ferrari's in the driveway. When I first went to Detroit, there was a couch in flames in the middle of the road and every house appeared to have been set on fire. I have never actually been to the Bronx but I hear a lot of rappers say a lot f bad things about it. I have also heard from movies and ppl who have been there that it is really bad. In Lord of War, Nicolas Cage says, "It is like parking your car in The Bronx, you just don't do it". So why is it certain areas of the United States are so badly neglected???