Nickelodeon didn't provide reasons as to why they cancelled Invader
Zim. There are rumors circulating online but they are just that,
rumors, however in April 2017 Nickelodeo…n announced an hour long TV
movie was being made. As of October 2017, airdate is unknown.
Most likely though it was cancelled for the same reason all shows
get cancelled that aren't ended by their creators or showrunners,
the ratings simply weren't high enough to justify the cost of
making new episodes. (MORE)