>>713577479
I got a theory that the less attractive a Serenity is, the stronger her power. Usagi's Silver Crystal is the strongest to date and her power exceeded everything else. Even up to the point where she fails against Chaos and becomes Cosmos, her power alone is the one thing keeping Chaos from winning in the far future.
The implications of that means Chibiusa dies and doesn't succeed her mother.
Real answer: Usagi loves junk food too much.