But do the consumers know that ebooks are durable goods and that the publisher has a monopoly on them?

In practice a lot of reader will just be looking for a hit for their dark academia vampire romantasy addiction. The book is essentially read once, and the buyer is perfectly fine with a different title. It's durable in the same way that a newspaper is, and the publisher has a monopoly in the same way that a used car salesman has a monopoly on the car with VIN f6d45280.

Similarly, the reader's perceived value isn't constant. A newly-released "part 1 of 7" of an unknown author (who knows if it'll ever even get a part 2) is less interesting than the debut novel of a well-established author. Likewise, demand can significantly increase due to the release of a spinoff TV series, or significantly decrease when the author is disgraced in some scandal.

There's only a true monopoly on things like college books, and there the demand has basically zero elasticity: either accept paying $200 for the book now, or fail your $2000 course. And those aren't exactly durable either!