That makes sense. Considering the resources required to shortlist candidates and interview them, companies would any day prefer to avoid it. Is there any relevant data, how many such jobs may exist that are not 'advertised'?
There is relevant data, but I don't know where it is, sorry.
I am under the impression that this sort of under-the-radar hiring occurs enough to be a significant cause of institutional racism in hiring. (If your existing employees are disproportionately white, and their friends and acquaintances are disproportionately white, then new employees who fill a position before it is publicly advertised will be disproportionately white; and this is without anyone being overtly or consciously racist, and without non-whites being discouraged in any way from applying.)
If you're disadvantaged because of your race, then it's racism.
It's important to be clear: the outcome is racist even when no individual is being racist. You can't be reductionist about this, you can't decompose the company into its individual employees and give any of them individually the blame for racist hiring outcomes. It's an emergent phenomenon: it is the company as a whole that is racist and the company as a whole that is at fault.
This is politically-correct/Marxist protelariat/bourgeoisie nonsense. The human race is composed of individuals, not "classes" at war with one another.
What qualities? You have said that no one there acts in a racist way. No "person of color" who applies for a job is treated unfairly. Thus no racism occurs.
You can only imagine racism there if you see the races as "classes" (i.e. in the sense of Marxist class warfare) and feel that each class (not the individuals within it) has a right to a "share" of the company (i.e. a quota of jobs -- regardless of whether anyone in a particular class ever actually applied for a job and was treated unfairly). I know this is what the leftist professors in schools of "grievance studies" are peddling, but they have tenure requirements to meet. What's your excuse?
If you don't have connections, you can't land a job that isn't advertised publicly.
Publicly advertising a job is tedious.