The answer is racism, see the story of Robert Moses [0]. [0] https://www.iheart.com/podcast/105-behind-the-bastards-29236...
Racism is real and a problem, but you could have an entirely all-white city in the US, it would still have this problem. In my own city, Austin Texas, the great majority of the homeless appear to be white. NYC has a black mayor, it hasn't (apparently, according to this article) made an appreciable difference.
[0]https://www.kqed.org/news/11943263/americas-highway-system-i...