Given that air travel is highly seasonal, and that airlines adapt their schedules [cutting routes, thinning frequencies, downgauging aircraft] so that supply does not exceed demand by too much [no point flying excess empty seats around the world on the peak-season schedule required for the busiest travel periods], could it not just be as simple as that this is one of the aircraft that is currently surplus to requirements, and enjoying a short break?

Not sure whether KLM handle these fluctuations, but it would seem more manageable to take particular aircraft out of use for a certain period where possible given the scheduling of operations, rather than having a set of rolling breaks of a day or two spread right throughout that aircraft type across the entire fleet. Even more so if maintenance or servicing etc can be performed during that downtime.