The law school rankings, for example, are based largely on how many students pass the BAR exam, and how many graduating seniors receive high-paying job offers - all pretty relevant info for someone looking to go to law school.
The research rankings for med schools are based largely on the amount of funding schools receive from the NIH. So sure, for someone looking to get into research, it's great. But to determine the quality of education you might receive there? It's not very useful.
The primary care rankings use, as a huge criterion, the number of graduates going into primary care specialties. What does this tell you, again, about the quality of education received at said schools? Nothing.