Had Nickelodeon made one rectifying decision rather than wasting the opportunity, the cult classic Invader Zim show may have had a much longer run on television. Instead, the two season-long animation staple was canceled by the children's network on the grounds that Jhonen Vasquez's Invader Zim simply fostered very low ratings. According to The Northerner in 2002, Nickelodeon went on record to confirm that the fate of the TV show was due to poor ratings from the channel's core demographic, kids ages 2 to 11, but rumors through the decades settled on Invader Zim getting the ax for being too dark.

https://screenrant.com/invader-zim-nickelodeon-mtv-move-save/