The fact that inventory is zeroed out on every single DL644/DL643 flight (currently scheduled as daily) from Nov 6th (start date) to Dec 17th except for the flights on Saturday is a pretty big tell this is not due to some sort of event and indicates a schedule change is in the works. Saturday-only schedules to leisure destinations is pretty commonplace as it tends to be the most popular travel date. There is still a separate daily non-stop flight on this route during this period.