That means that the smart thing to do is buy them as you read them, and not hoard them.
That doesn't track with my experience at all for a number of reasons:
- Smaller bookstores who may or may not be an official part of the publishing supply chain stock smaller amount of copies of a given book. Once an edition sells out, they might not even have the means to restock/order from a new batch of printing.
- Even big chain bookstores have to consider supply and demand economics when stocking their shelves so even them can't guarantee "perpetual availability" of a title.
- Not to mention, books go out of print, even way before they go in the public domain. The best way to get a copy is by accident in a thrift shop. If I encounter one I really like, the best move for me would be to buy it then and there, my current reading queue be damned.
- Admittedly, acquiring books is easier now due to Amazon, et. al., but we are still very from from being able to acquire a book when you actually want to read them. Not all books are available to buy online!
And this is one of the major benefits of e-books: you can postpone the purchase until about 15 seconds before you want to read the book.
Can also be done at bookshops.
The point is that them being present in your library serves as a physical reminder that you might want to read them (whereas otherwise you’d forget about them), and when you decide you want to read them, you can then do it instantly. As others have noted, it also avoids the problem of books having gone out of circulation.