The government workforce has been aging out, and many have the 4 weeks of annual leave that happens at 15 years of service. The Gvt also caps annual leave at a certain point, creating a use or lose situation at the end of the calendar year.
So we really need more data to figure this out. But in the absence of it I’d peg it on a combination of use/lose use at the end of the calendar year, plus weather related closures.
Sorry, it’s actually a little more than 5 weeks per year.