Shadow libraries are a competition to the official ways to access the papers.
Just like in any market, the various offerings have advantages and disadvantages.
- Advantage of, say, Elsevier website: is legal
- Disadvantage of, say, Elsevier website: accessing costs money (even if your university pays)
- Advantage of, say, sci-hub: is free
- Disadvantage of, say, sci-hub: accessing is somewhere between legal grayzone and illegal, depending on jurisdiction
As in any market, by your choices, you decide which offering you prefer:
- If you decide to get the paper from Elseviert (even if you can access it "for free", because your university pays), you vote for "Elesvier's business practices are perfectly fine."
- If you decide to get the paper from sci-hub, you vote for "what sci-hub does is less evil than what Elsevier does."
Choose the market offering that fits your alignment.
Also, there's always that one guy that everyone knows that you can just email obscure paper requests to and he'll send you a PDF almost immediately. And of course you never ask how that works. But it works.
As such, there's little to lose if a university cancels their official Elsevier subscriptions. Their student's won't mind. And I believe that is why universities haven't banded together.