[cooperadymas]

Libraries buy the e-book legally and loan it out to a single person who then returns it. Libraries are often forced to buy ebooks at a much higher than consumer price, supposedly to offset the cost of customers who would buy the book themselves if libraries didn't exist. The author/publisher get paid for every copy purchased by every library and no more than 1 person can be reading that copy of the book at a given time. If someone wants to permanently add it to their collection they must purchase it themselves.

It's the functional equivalent of someone buying the book and then passing it on to the next person who wants to read it.

With pirating, perhaps one person bought the book originally and then it gets sent to an infinite number of people who permanently have it in their collection. The author gets paid practically nothing.