[harshreality]

Voyage to Arcturus and most if not all of Alice Sheldon's (aka Tiptree's) stories look like they're in print, and published as ebooks (and on pirate sites if they're not stocked by your local library). Open Road and Gollancz have been publishing a bunch of older science fiction like that.

Buying out copyright for books that a publisher is selling would be much more expensive. A few million dollars wouldn't go very far if every copyright holder wanted, for instance, a modest $5k per book to buy out their copyrights. And why would they sell their copyright for pennies, particularly when they already bought out the copyright from the original publisher? They put in all the effort to re-publish the book, and marginal and up-front costs now are zero (ebooks) or low (print on demand).

It's not obvious that making obscure books available for free would be doing them any favors. With the avenues of libraries and piracy available, having a non-zero price should help boost the perceived value of the books.