Evidently Warner Bros, which released both Ready Player One and Blade Runner 2049, wasn’t keen on the former stealing some of the latter’s thunder (regardless of distance), hence why Penn had to use The Shining as a replacement.
Blade Runner 2049 was released on October 6, 2017, so had Ready Player One stuck to its original release date, there only would have been a two month interval between the movies.
But as Penn also noted to The Playlist, he wishes he still had been able to include a few Blade Runner references in Ready Player One, even if it had been something as simple as Rick Deckard’s firearm, which Parzival, Art3mis or one of the other protagonists could have broken out during the movie’s climactic battle on Planet Doom.
Ready Player One was originally scheduled to come out on December 15, 2017, but it later moved to late March of this year so it wouldn’t have to compete with Star Wars: The Last Jedi.