Some of it is likely due to "organic" stratification and segregation of society, which is a less-nice way of saying people keep to their own circles. Some of it may be deliberate discrimination due to factors such as attractiveness and access to resources, often obscured by information asymmetry in the hiring process. Some of it may be that these businesses tend to be located in more prosperous areas that are both distant and difficult to access to by people who lack reliable transportation.

Several of these factors, while alone may not be significant, can occur together to striking effect.