With Star Wars moving away from the December release schedule of 2018, seems like the month needs a little pick me up. Maybe that is why Sony pushed the animated Spider-Man movie to that month.
In April, Sony Pictures chairman Tom Rothman announced the animated movie and said “The film will exist independently of the projects in the live-action Spider-Man universe, all of which are continuing.”
Originally, the animated movie by LEGO directors Phil Lord and Chris Miller was to be released on July 20, 2018, but with the Summer movie season becoming more crowded, it may have been a good decision to move the release date to December 21, 2018. Also, no other film has been slated for a December release, yet.