Part of why this happens is that, in any medium, most works aren't very popular. A few years ago, someone who worked at YouTube told me that more than half of YouTube videos had zero views — not even the uploader had watched the video on the site. Most blogs have only one reader or a few readers. Most software projects have only one user.
Look at the things that someone has taken the effort to transcribe/index/classify, like the 9,785 books published in English in 01927 with full view available on the Hathi Trust website whose titles contain the word "A": https://catalog.hathitrust.org/Search/Home?adv=1&setft=true&...
• The trustee and the A. L. A.
• The influence of hydrogen ion acitivity upon the stability of vitamin A
• The national cyclopedia of American biography : Current volumes A-
• A study of English drama on the stage / by Walter Prichard Eaton.
• The nations of the world : a pageant designed to show their contributions to civilization / prepared by the faculty of Public school 53, Buffalo, New York ; illustrated
• A book of shanties
• A book of prefaces / by H. L. Mencken
• A January birthday party / by Jack Bechdolt & George Illian
This last is a sort of instruction manual for throwing children's birthday parties. In January. It includes things like a cake recipe, suggested menus ("Hot Fricasseed Chicken. Hot Biscuits. Cranberry Sauce. Birthday Cake. Ice Cream. Chocolate Milk Shake. Candies. Nuts.") and tips for hanging crepe paper from plaster walls into which you cannot drive a nail or screw.
This kind of schlock, in aggregate, is immensely valuable as a window into how life has changed over the past century, but this particular book is extremely replaceable. If you were allocating limited resources to providing access to either A January Birthday Party or something like Harry Potter and the Philosopher's Stone it would be criminal to choose the former over the latter.
Yet that is what the current copyright laws require us to do.
This is not to deprecate Jack Bechdolt and George Illian; writing a schlocky easy-craft-tips newspaper column or book with cake recipes and unoriginal children's game ideas is a perfectly fine way to spend your time, much like baking a trout or unclogging a toilet. Surely publishing the book was, overall, beneficial to society, even if only slightly. Nothing suggests that https://en.wikipedia.org/wiki/Jack_Bechdolt or https://www.wikidata.org/wiki/Q52156792 was anything other than a perfectly decent person. But that doesn't mean that preservation of the product of their activity is worth spending extra effort to preserve a century later, any more than the baked trout or the toilet clog would be.
I'd say that about 90% of the items in the Hathi Trust query result I linked above are of similarly insignificant value.
Even cultural works that have some enduring value on their own (I suspect The national cyclopedia of American biography and A book of shanties fall in this category) are not fungible with unavailable ones—no quantity of books of 19th-century folk tales forms an adequate substitute for the second edition of Sedgewick's Algorithms¹, nor vice versa.
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¹ I was dismayed to be unable to find the second edition when I was writing https://news.ycombinator.com/item?id=45571196 the other day, and I believe that this problem is mostly a result of its copyright status.
