In the case of Art Thieme, Kicking Mule was sold and the company who bought them own all rights to his albums, two of them if I remember right. He cannot reissue them on his own and they will not. We had a letter-writing campaign years ago to try to get them to.

Also, even if an artist is dead, there may still be an estate which collects whatever royalties there may be, so just because they are gone doesn't mean the product is up for grabs, free of charge.