Both Zutara and Narusaku had parallels that ended up being only seen by the shippers
Both Zutara and Narusaku are friendship stories that had chemistry
Both were teased (Anime filler for NS, season 3 trailer/magazines for Zutara)
Both needed two other ships to die for it to happen (Maiko=Sasusaku, Kataang=Naruhina)
Both had the ending spoiled before the official release by outside sources, and both had fans ignore/explain away the spoilers before confirmation
Both had long shipper manifestos that ended up being overthinking/over analyzing
Both had a resolution that had no explanation/just happened (Katara was confused/Needed time after the forced kiss until the finale skipped any resolution on this, instead she just kisses Aang out of the blue/Naruhina children)
Both had characters that loved the other character from the start and never wavered (Mai=Sakura, Aang=Hinata)
Both had one ship explained in another source (Maiko=the comic after season 2/Naruhina=the movie)
Both were alike (Naruto/Sakura wanted acknowledgment, Zuko/Katara had mothers taken by the fire nation and it shaped their future)
Both had friendship events/stories seen as romantic (Southern Raiders/Season 2 finale/CPR/Healing scene)
Both made more sense to the shippers, despite not being canon in the end (We're kind of like Harmony now, too lol Harry ended up with a side character, his friends got together)