Donald Glover had done a splendid job for FX when he created Atlanta, and a lot of people were excited to hear that he was working on an animated Deadpool show. The show eventually ended up being cancelled before it even aired, and it turns out that it was Marvel (and not FX) that decided to pull the plug on the show.
FX CEO John Landgraf told Deadline:
"Marvel controls the IP and the decisions around the IP. It was their decision not to go forward with Donald and Stephen's version, I personally liked it."
As for the reasons that Marvel decided to axe the show, we don't really know, but hopefully there's some room in the future to reconsider the Deadpool series. After all, the two DP films have been smash hits. It would make sense that they would want to bank in on an animated series.
With the Disney/Fox merger already approved, maybe Marvel Studios can have a more hands-on approach when it comes to bringing Deadpool to the small screen in the future. Besides seeing just Deadpool in his own movies, a lot of fans have been itching for a team-up with characters like Spider-Man and the Punisher.
Fingers crossed Donald Glover's Deadpool show gets picked up in the future.
See Also: Daredevil Season Three Confirmed for Second-Half of 2018