Libraries buy copies (and the creators get paid). And the copies (on average) circulate a lot less often than you'd think. High volume authors would probably

Libraries buy copies (and the creators get paid). And the copies (on average) circulate a lot less often than you'd think. High volume authors would probably opt out of the library system if they could, but the average author probably gains from libraries (since they buy a bunch of copies that otherwise wouldn't be bought).