I think because of the plot of the game. When a game over happens your character goes through it and then time warps back to the morning of the day it happened with only subconscious recollections of what happened. If you hadn't slept, then it would be the same day you did anything before that game over. Meaning those events within the story of the game haven't happened.I wonder why don't they just make the event auto-saved once you triggered, but bring up this extra hurdle in an already very confusing game.
And the main plotline is trying to figure out who cursed you with this time warping reversal magic and why. Since some of the other characters can slightly notice the memories from other timelines and the most powerful characters like Diakor just outright know what your powers do because he can remember all the other timelines more or less. Though he doesn't know how or why.