There is really no qualitative difference between a bought ebook and a borrowed ebook. If it's just as easy for me to borrow a book, and just as good, why would I ever buy any?
It seems obvious that publishers and writers would be concerned about that.
Physical library books reach out to the demographic that can't easily buy books; the people with more time and less money: the young, the old, and the unemployed. Ebooks don't really discriminate in that way. If anything, the public purse and the publishers and authors are subsidising people like me, who have jobs and disposable income (or, okay, in my case, mainly access to credit.)