WWE TLC will be taking place on December 15th and with the company not having much time left, they needed to make as many matches as possible. One such match was apparently a change in plans.
On Wrestling Observer Radio, Dave Meltzer said that The Revival were not initially going to challenge for the Smackdown Tag Team Titles at WWE TLC. Robert Roode and Dolph Ziggler were originally planned to be the challengers. However, owing to the fact Roode and Ziggler were busy with King Corbin and Roman Reigns, this change was made.
So The New Day will be defending their Smackdown Tag Team Titles against The Revival at WWE TLC, which is sure to be a solid match.