[sertraline]

May be because they are not reselling anything. As far as I'm concerned, in a legal world you cannot get your textbook without paying first. Z-library gives you these books for free. If you reached your daily limit, you wait 24 hours. No one really forces you to get into membership and there are other, free ways to avoid the daily limit. By your logic they either must provide copyrighted content for free and pay hosting out of their pocket or provide nothing at all since they don't have the moral ground to ask for money. Servers cost money, a lot of money.

[some_random]

You seem to think that because they give 10 books a day, somehow charging for the 11th onward doesn't make it a commercial operation? And yes, I think that if you're going to be hosting material in violation of copyright distributing it for free (or asking for voluntary donations) is the only remotely ethical way to do it. Otherwise, you're illegally profiting off of other peoples work.

[sertraline]

I don't know what's hard about understanding "daily limit" model. If you can't download 11th book, just come back tomorrow and you can download 10 more books. You can download 10 more books the next day after that. You can download infinite amount of books, downloading 10 of them every single day. This is what "daily limit" means. Now, "charging" means there is no other way to download the 11th book unless you pay. There will be no way to download it tomorrow, or the next day after that, unless you pay. This is "charging". Their membership model is no different from donations, except that membership gives you benefits. You are NOT forced to get it.

[skyyler]

The fact that you can pay and get something in exchange for the payment makes it a commercial enterprise.

It's very simple.

Libgen isn't facing the same issues because it isn't a commercial enterprise.