IANAL but Z-Lib is run as a for-profit business which makes it more of an open and shut case, especially if they're hosting their own files (which I believe they were, to implement that pay gate).

LibGen acts more like an archive that's hosted on IPFS which eliminates a lot of the liability and can't realistically be taken down. You can only download the books from the mirrors LibGen links to and they're often just IP addresses so there's no DNS zone to seize.

I believe a significant difference between the two is that Z-Library actively asks for donations in return for more features, whereas Library Genesis does no such thing AFAICT.

They are definitely not better known among normal people -- Z-Library was trending on TikTok massively (this is what prompted the aggressive arrests and seizures lol)

It is possible that Libgen's proprietors are known to law enforcement but never stepped within reach of Western legal authorities. Certainly, had Z-Library's staff all stayed within Russia, they never would have been arrested.

I think Z-library attracted more.users because of its UI. I also like Libgen