Too often, the authors die without setting up a literary estate (and often ages before ebooks were an option). Sometimes, their families don't want or allow the work to be reprinted, so it ends up in legal limbo. (That happened with J. N. Williamson, I think, and possibly John Steakley.) Sometimes, there are simply no heirs. (In the case of Ruby Jean Jensen, people thought she had no living heirs, and the reprints came out once they realized she did have living heirs.)
There was an episode of The Horror Show with Brian Keene about that. If this is the one with the story about J. N. Williamson in the nursing home, it's both sad and rage-inducing.
https://thehorrorshowbk.libsyn.com/t...n-keene-ep-163