Plans clearly changed, and since then the character has made appearances in Guardians of the Galaxy Vol. 2, Avengers: Infinity War and Avengers: Endgame.
Karen Gillan has become an impressive action star in her own right in the past few years.
That work showcased her ability to be a blockbuster star, and certainly must have been a factor in her being cast in Jumanji: Welcome To The Jungle.
Gillan was only supposed to be on set as Nebula for eight days before her character was originally written to die.