Researchers don't get paid by journals for their submissions. In fact, it's usually exactly the opposite: most of the big ones have submission fees.
This is why I don't really have any sympathy for the publishers affected by Sci-Hub, when at the same I strenuously oppose software/game piracy. I just don't see what service they provide: they don't pay the researchers, they don't pay the peer reviewers, and they don't validate the papers beyond basic copy-editing and typesetting. They're just useless middlemen who provide no utility. I'll be spitting on their grave when we finally get rid of them.
Elsevier had a 36% profit margin last year, which is a pretty clear signal that they don't face sincere costs or competition.