On the web, I find a review of an interesting-looking book on cake-cutting algorithms. The review cites The Computation of Fixed Points and Applications by M.J. Todd (Lect notes in Economics and Math Systems; Springer-Verlag, NY 1976). Now, that in turn looks like a book I should be interested in, BUT, it's not online, and it's not in the library.
Well, I could request it by inter-library loan, but that's too much hassle for a book that may or may not turn out to be useful. Maybe I can buy it using money from a research grant, but even if a copy can be readily bought, will it be worth it, even if there's plenty of money in the grant? (And, that's also hassle.)
No-one really expects to make a profit selling this book right now, do they? (Maybe 30 years ago, you'd be ripping someone off if you copied it illegally.) But, copyright law, and in particular the absurdly long duration of copyright, prevents anyone from putting the book online. The result is that I probably won't ever read it, and the book will effectively vanish, at least for another 60 years, or thereabouts, when it may get to enter the public domain.
Of course, the above is just a specific instance of a general problem that recurs time and time again. Not just in a professional context either -- there are lots of miscellaneous books I've headr of and wanted to look at, which are not profiting anyone as intellectual property. If I write a book, I would want it to enter the public domain after about 10 years after publication.