I don't want to claim that NOLF is comparable to Zork, and without a doubt times have changed a lot since then, but it comes to my mind that it's a notable fact that even half forgotten and seemingly out-of-fashion IP can be much more valuable than anyone at any given time assumes.
Namely back in 1992, having the rights to Infocom's catalogue, which earlier had been put up for grabs for 25k, literally saved a then bankrupt Activision (!) when they rereleased it as a compilation of The Lost Treasures of Infocom, for millions of revenue in total. [1]
In addition to the problems and cost of establishing ownership that other people mentioned, I suppose this story was one hell of a lesson for any publisher not to forfeit any rights you may or may not be holding.
Namely back in 1992, having the rights to Infocom's catalogue, which earlier had been put up for grabs for 25k, literally saved a then bankrupt Activision (!) when they rereleased it as a compilation of The Lost Treasures of Infocom, for millions of revenue in total. [1]
In addition to the problems and cost of establishing ownership that other people mentioned, I suppose this story was one hell of a lesson for any publisher not to forfeit any rights you may or may not be holding.
[1] https://www.filfre.net/2019/04/an-unlikely-savior/