It is a commonplace that the politics of cities is often dominated by bribery and machine politics. The question is why is this? Several answers present themselves, including insufficient political competition (cities are uniformly Democratic), lower social cohesion (as every ethnic group and cultural tribe wants its slice of the pie), or simple proximity of spending and contractors, making it more likely for sweetheart deals to get done.
My theory is that cities are more welfare-state-like, with high taxes and generous handouts and government spending. This larger government, coupled with the higher density of interest groups that form in ethnic enclaves and business groups, leads to politically-connected insiders getting goodies for their tribe and skimming a little off the top.
(Yes I’m sure you can pull up corruption scandals anywhere in the country, but while such scandals do happen in Podunk County, they’re big news and therefore rare, while it’s practically the norm in urban areas. When the left-wing writers of The Wire treat it as a commonplace, it’s a commonplace.)