That was my point, only I put a blunt edge on it, unfortunately.
Although public libraries keep some old books in their collections, many, many more are safely in the hands of private individuals, either as family heirlooms or because, like you and me, we like to have them. And I am not talking about only "collectible" books, either. I mean books that are no longer in print, and many that are no longer in your local library due to "excessing."
Since a library's budget is not unlimited, they routinely sell off or otherwise dispose of books that haven't been checked out in a while or are "obsolete." (My local library is remiss in getting rid of ancient computer reference books. Who still owns an Atari or a Commodore 64, much less has a need to learn BASIC for it? Yet they're still on the shelf.) What they replace them with is, apprently, dictated by some board which second-guesses the reading habits of the library's patrons, or viewing habits in the case of video.
The overwhelming trend is to buy new stuff, recycle the old, and cater to the "majority" (except where it comes to political and social issues, where of course a loud minority demands more-than-equal representation in the selection of materials) to ensure more funding from the city next year.
Preservation of books, tapes, magazines, etc., seems a neglected function of most libraries, which exist only for the here and now.
This is why I make a point of stopping by and seeing what the library is disposing of.
A recent aquisition included National Geographic Magazine, bound in 6 month volumes from 1914 to the late '50s. My wife had a mild fit when she saw all the heavy boxes, but I have been enjoying picking through them, especially the older volumes.
I wish I had twice as much house to keep them all in (those and the tons, literally of other books bought there and at rummage sales, auctions, and flea markets).
Online books are fine, I guess, but there is no substitute for vintage hard copy. It does not change in content, and does not sway with the political wind.
Books acquire a lot of character through the years, especially the old ones.