At least in Germany a lot of research isn't being done at universities but at dedicated research institutes. Quite a few PhD students are working part time at uni and part time at one of the Fraunhofer Institutes or at Forschungszentrum Jülich. Another European example is CERN in Switzerland.
This model just doesn't conform with all those research university rankings.
American Visiting Researchers at CERN, since they remain attached to their Universities, probably count toward their institution's ranking. But a full time researcher at CERN doesn't.
The JPL at Caltech and the Lincoln Laboratory at MIT are the opposite of that. They do, what could be considered mostly government research but I'm sure 100% of their citation count goes toward their respective institutions.
Or even more importantly the Max Planck Institutes and Helmholz.
Max Planck society is a heavy weight for sure and the co-operation with universities pretty unique as they need each other and are fully public (other than e.g. American private entities like JPL).
This model just doesn't conform with all those research university rankings.