There are many reasons why an actor wouldn’t return for the sequel to a hit movie they made.
Sometimes contract negotiations fall through; sometimes there are creative differences between performers and filmmakers; and sometimes the story being told moves away from specific characters.
In the case of the upcoming Don’t Breathe 2, it’s a bit of Column C that explains why the film doesn’t feature the return of Jane Levy’s Rocky, the protagonist of the original – but there is also another reason in the mix as well, and it’s one that you would probably never guess: apparently writer/producer Fede Alvarez didn’t want Levy to come back partially out of concern for the effect that the effort would have had on her.