Because, when we define “justice” in general terms and “social justice” in sociological terms, we bifurcate the two and see the biggest problems in the urban context. This is a mistake.
Here’s why: the word “justice” is no different than “social justice” in biblical categories — just run your eyes quickly through Exodus or Deuteronomy or the prophets (and don’t just go to Micah’s famous text). There you learn that “justice” refers to “what is right” (say, tsedeqah or mishpat) and what is right is determined by “what God says” (Torah) and behind what God says is “who God is” (the perichoretic splendor of love and holiness and beauty). So, in biblical categories “justice” is indistinguishable from “social” justice because it is the Nature of God that determines — we are talking ontology here — what is right because God is What is Right.