Is the idea of staggered elections to keep some continuity? Running a council isn’t easy and perhaps potentially replacing the entire thing in one go is problematic? Can’t imagine replacing competent councillors with a bunch of the local headbangers who signed up to Reform because they thought the boats needed to be stopped from coming to their landlocked county in the midlands is a good idea.
Doesn’t explain why London boroughs have all their seats up at once though.
As I understand it, there is local government reorganisation (simplification?) due soon so some of those voting now will also be doing so again once it happens.