I wouldn't include the "prevent them from sinning" part. Traditionally, Ammit doesn't want to keep you from sinning - Ammit gets to eat the hearts of those who have sinned. You sinning is good (and tasty) for Ammit.
We could speculate why she's been waiting for people to die naturally before, and now isn't. Maybe with the creation of the multiverse, the walls between Here and There are weaker, and she no longer has to wait for death? Or there's now more competition, so she's desperate to eat?
Anyone here ever try to get a modern high definition movie camera rig into a legitimately small apartment? They're inappropriately large because that detail is less a problem than shooting in small spaces.