No confusion at all. Your public library, fueled by your taxes, pays a fee to the publisher every time you borrow an ebook (or some similar payment system which recognises concurrent use). Just as your library has to buy 10 copies of a book to loan out to ten people at once (the 11th .. and 52nd ... have to wait in line), your library buys a certian number of ebook licenses and, when they are all in use, the rest of us wait in line.
You can rectify this: lobby your municipal council to tax the citizens more and hand larger annual grants to the library system.
Or, enjoy the library system by reserving and having a surprise title make its way to you in the future and, in the meantime, shop at kobobooks.com for something to read today.