Suppose whoever is in charge of making wants to tell the exact same story with a new cast, possibly a new location. You’re in charge of picking the songs for the movie.
You magically have access to the rights of any song ever, the only limitations is that the songs should fit at the same points of the same story as the first movie.
Do you use the same songs? Would you run with a different genre? Change decades? Swap in different Abba songs? Is it sacrilege to even wonder?
It would not be Mama Mia without the original Abba songs.