I mean what is there for them to relate on? Zuko is this grand redemption tale that connects with the main villain and hero while Toph is the least relevant member of Team Avatar outside of Suki (who wasn't relevant for most of the story anyway).
Toph's backstory is the most relatable, its no where near as dramatic as the others. Aang losing everything, Iroh losing his son, Zuko losing his honor, Katara and Sokka losing their parents. Toph was just a spoiled girl who got rescued, and Zuko called her out on it in an episode.