One thing to keep in mind is Detroit received Italian immigrants in the tens of thousands, while Chicago received them in the hundreds of thousands, and New York City, let alone the East Coast in its entirity, likely millions. (Four million total Italian immigrants to the US from like 1850-1920s, when it began to peter out.)

So I'm not sure how long a city with a relatively small Italian immigrant population three, four generations in, and virtually no Italian community to speak of, could be expected to support a mafia branch.

Interestingly I was just reading about it and apparently the closest thing metro Detroit has to a "Little Italy" is a small string of Italian stores and restaurants along Garfield Road in Clinton Township.