Do you have evidence they are profiting? I'm genuinely curious how these kinds of archives sustain themselves.

I don’t think any of them are breaking even when you consider the maintenance costs, I just thought it was kind of funny considering the nature of the line of work they are in.

This was a different group of people but when some of the old LibGen domains got seized the FBI uploaded photos of the owners and the things they had spent their money on; a crappy old boat, what looked like a trailer in rural Siberia, and a vacation somewhere in the Mediterranean. It honestly read like sketch comedy, because the purchases didn’t appear remotely ostentatious.

Z-library also supposedly caps downloads at 5 per day and offers more and faster downloads to paying subscribers.

They take donations.

Just to nitpick, that doesn't imply profit. They could be breaking even (and probably are working at a loss).