You're right Anthony, I don't have any special evidence to support my position.  Do you have any to support the belief that libraries actively use Sci-Hub as a means to support journal cancellations?  I’ve been in the field for over 20 years, gone to countless conferences, read uncountable list-serv posts and have yet to see or hear any librarian say they rely on and intend to cancel journals based on either of those sites.  Possibly I missed that session or thread, but I honestly don’t believe so.  I think a session on that would be fairly well attended just to hear what someone had to say and how they could justify taking that position.  No, the sessions I have seen and attended that mentioned Sci-Hub were always about how to stop that site from downloading articles from our campus networks.  That seems a VERY strange session to have when libraries are actively using Sci-hub as a budget relief option.

No, the argument libraries rely on those sites seems more like someone is scrambling to understand how universities could cancel their contracts with them.  I think the publishing industry find themselves in a situation where the industry they rely on is seriously considering ways to walk away from them completely and are looking for any reason that makes sense. The publishing industry seems to have completely forgotten that they are a service industry to academia, not the other way around.  Academia is not there to service the financial needs of the publishing industry.  The publishing industry is there to package the content academia produces and then to distribute it back out to other academics.  

A better question would be why some publishers refuse to see the writing on the wall when every year libraries publish annual reports and articles  saying “library budgets continue to shrink” and “publisher prices continue to go up” for 30+ years.  If you’re looking for the reasons the current run of library cancellations are happening just look at the base economics.  30% profit margins and average annual 7% price increases.  Strawmen arguments are not going to change the base economic reality.  Librarians have literally been warning publishers FOR YEARS that the situation was unsustainable.