Just because a school has access to the information doesn't mean they have the expertise, time, or money, to turn that information into a number that can then b

Just because a school has access to the information doesn't mean they have the expertise, time, or money, to turn that information into a number that can then be used in admissions. Admissions tests have existed for centuries the idea of the SAT is by having a single standard you can have one group of people make a better test for less money (and student time). This is very much the same thing, figuring out how to rank high schools and estimate adversity by street address for the whole nation is a HARD problem.