It might be because 100% of the content on SciHub is owned by monopolistic copyright trolls that serve no purpose other than rent seeking. Libgen is diluted by content owned by businesses that perform some level of curation, pay authors, sell direct to consumers, compete with each other etc.

Those businesses have better things to do than piss off their customers and authors as they try to police the internet.

Even more cynically (and predicted by Max Headroom ~35 years ago) academic work has more potential to unlock economic value for the unwashed masses, so it needs to be better policed.