I don’t see where there is evidence of “data mining” and misuse of the data that the OP claims exists. It is used as part of holistic admissions. I have not heard of any cases where universities are selling that info to third parties (that would be what data mining is really for). You are casting aspersions, implying nefarious actions by college admissions offices – please provide evidence if you have it beyond the use already discussed here of evaluating the whole picture of a student’s background.
And also, regarding why not just ask what degree parents have, as an example, I personally draw a distinction between a student whose parent went to Harvard Law and one who went to a law school ranked in the 300s – and if you are applying to top schools that are not H, that info still matters in placing the student in context.