The progression with most other fast food chains in CA was that once you start hiring employees who don't speak English, then you have to have all shift managers be Spanish-speaking, leaving no upward path for line employees who aren't bilingual. Before long, most of the kitchen crew is non-English-speaking.
They don't have franchises like the other chains.
I don't think that's a factor. Both corporate-owned stores and franchisees use the same employee demographics, generally. Sometimes you'll find a franchisee who is an immigrant from outside the Americas and find a lot of family members and their friends making up the crew. (For example, there's a local Taco Bell that has more South-Asian employees than not.)- every In-N-Out must be within 500 miles of a beef distribution center [1]
- In-N-Out tries to buy it's land [2]
My impression is that they grow the business from cash flow, not debt, and they move slowly so they can keep up quality. They are a privately held company, so hard to verify some information.
[1] http://www.ocregister.com/articles/accelerates-291670-expans...
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.