“We had always mentioned it was limited but with no explicit end-date,” wrote developer Timi Studios in Reddit. “We wanted to see the reception, see the feedback, and see how we can potentially shape the mode for the future,” he adds.
The developer also expressed that the Zombies mode did not reach the level of quality that they’ve desired. Furthermore, the mode’s second map Nacht Der Untoten will not see a global release due to this. However, Timi mentioned that the mode will likely to return to COD: Mobile again in the near future. He adds that they’ll reintroduce Zombies, along with the Nacht Der Untoten map, once they’ve made sure its quality has vastly improved for player enjoyment. (Source: COD Mobile sub-Reddit)