I guess because they don’t know sh*t from Shinola.
Well, actually they do, and they’re bringing back the old brand name that’s gone unused. And they’re doing it all in Detroit, which is a gutsy thing.
But yes, the Shinola Cosmetic Company used to be best-known for various men’s cosmetic products, and shoe polish. It’s the shoe polish which the idiom is talking about.
The old Shinola company was actually from Rochester, New York, if my sources are correct.