It also seems to be a great way to explore how the players are and aren’t aligned. Because you can trigger Faction Moves by working with or against members of various factions.

And, well, Debt Moves let you mark Factions as well, and so does starting up trouble with Factions (Hit the Streets, Face to a Name, Investigate a Place of Power). So it all keeps that engine going and uses the Factions as poles that the MC can use to ground and shape the city.