In a recent appearance on The Tonight Show Starring Jimmy Fallon, Zombieland co-star Jesse Eisenberg admitted that this was a major factor in the Zombieland sequel delay, because everybody involved wanted the original writers to handle the script for the new movie.
The first Zombieland movie was written by the dynamic duo of Rhett Reese and Paul Wernick, and while the pair had long been considering a Zombieland sequel, the two got a bit distracted in recent years as another project of theirs, Deadpool, became an even bigger hit that spawned a sequel that was put on the fast track.