Recorded material is quite different to books: you can't really copy a book. OK you can scan all the pages - a lengthy job - but you can't reproduce the binding, covers, feel and smell of an old book. Digitalisation makes copying easy: hence those friendly messages at the beginning of a DVD threatening you with a visit from the FBI and a chance to see if Lead Belly songs are still sung in federal jails.
I quite understand copyright but it leads to greed as shown above and, even worse, a ridiculous dog in the manger attitude depriving the public of a chance to hear historical recorded materials. It took the BBC over 60 years to release those Woody Guthrie recordings from the 40's: you couldn't even pay the engineer's high fee for a copy. And they have never released the Cisco Houston recordings made in the 60's.