It's managing the grumble. Get it announced as one ac year ends, give everyone a chance to absorb, digest, express opinions, everyone has a summer away, old news by Reform, older news by this time next year, and builds in a year to plan for orderly execution.
I don't know whether this is all plebes scattered across the Brigade method or batch swaps by company. There have been variations when it occurs after youngster year. It also allows for incoming midshipman leadership to take ownership of the change and be challenged to plan and execute it in a positive manner. Dant is likely looking at this as a developmental opportunity for new stripers.
Plus ça change, plus c'est la même chose.