This is a New York-centric view; It doesnt matter if New York is a bigger city, Like Alfa pointed out, detroit was integrated at the production, supply And distribution levels, so they control thier own production, transit, (with the Teamsters) And distribution, the most powerful drug syndicates are almost always horizontally and vertically integrated like this.
Its why you saw the sicilians sending thier own guys to move the dope over here, why the colombians sent thier own guys to move dope,why CN imported Puerto Rican immigrants to move dope for them (something i read recently, actually kinda explains Nelson Cantellops and Vito, to me at least)why you see ndrangheta making moves on the New York market. New York might have had control over distribution and an entry point,( the docks) but detroit had the links to producers, and had family in the mafia in sicily, trusted people to handle it on the other side of the water.
You can control production like a Luciano, you can control distribution like a Ormento, you can be the middle -man linking both Bono,Galante, Rizzuto, maybe Cali now, But if have all three, you are a King.....