I take it you don't know many government or union workers? What evidence do you want? Find one and have a conversation with them. You'll discover that this is c

I take it you don't know many government or union workers? What evidence do you want? Find one and have a conversation with them. You'll discover that this is common in most any workplace where PTO converts to actual dollars. Much of the private sector, and especially tech, doesn't operate under that kind of system, so it wouldn't make sense for those workers to do it, but in ones where it does it's definitely common to bank some fraction of one's annual PTO with the expectation that it will become money, at some point (often retirement). It's not at all unusual for mid-career workers in those work situations to have several months of PTO so saved.