[sotero32]

Shouldn't the purpose be to help prospective graduate students evaluate the strength of PhD programs in the fields they are interested in?

I think that excluding research in companies or universities without PhD programs is much different than excluding EE/ECE professors who happen to be at universities where the bureaucracy makes it difficult for them to have some sort of "official" appointment in the CS department. It is also much more rare that these entities publish in the top-tier conferences that csrankings counts.

Note that it is not just professors who can advise CS PhD students, it is professors who can SOLELY advise a student for a CS degree. It would help even if EE professors who have co-advised CS PhDs at the same university were allowed to be included.