The standard of living for retirees tends to change, for example;
Their expenses go down after they retire. This is because they are no longer working and have less need for things like work-related clothing and transportation.
Their health costs go down after retirement. This is because they are no longer working and are no longer exposed to the stress of the workplace.
Their social activities change after retirement. They may no longer be able to participate in the same activities as they did when they were working.