Here's why:
* The movie focuses on Aang's journey: The live-action movie is primarily about Aang's journey to master the elements and defeat the Fire Lord.
* Toph's story is later: Toph's introduction happens later in the Avatar: The Last Airbender series. It's likely the movie will focus on the main characters introduced in the first season.
* No official casting: There have been no official announcements or casting news for Toph in the movie.
However, it's always possible that Toph could make a small cameo or be introduced in a future sequel.
It's best to wait for official announcements and updates from the movie production to know for sure!