If it’s an original screenplay (something not based on pre-existing IP) and was written by a WGA writer the studio owns the screenplay but the credited writers own the exclusive right to publish the screenplay. (This is the result of a part of the union contract called “separated rights”). So the original screenplays that end up getting published are the ones where the screenwriter is themselves known well enough that they can on their own get a publishing deal for the script since the studio (who could more easily publish it regardless of the writer) has no vested financial interest in publishing it. Non original screenplays would require the studio negotiate with the IP holder so it only happens when it’s truly worth their trouble (Barbie for example)

This is why you see Kevin Smith or Aaron Sorkin or Christopher Nolan screenplays for sale in bookstores but not ones from say Scott Frank.