I suspect the answer is simple - the trainers haven't scratched from the finale because they don't have to yet. They are hedging their bets in case some heavy rains appear and the final race really does get taken off, even though no one thinks that will happen. Many tracks don't require that all scratches be in before first post, only a certain number of hours before the race in question gets run. (Bettors don't have to place their bets the way we have to make our picks
).