The terms under which libraries lend out e-content are awful: e-content expires after either a given number of lends, a period of time, or whichever comes sooner, while a well-maintained library book can last for decades, and it tends to be more expensive than its analog counterpart (eg: an e-book for may cost more than its heavy-duty library-style-binding hardcover).

That said, the key difference is that book publishers decided to offer e-content under an explicit license, while game publishers have not.