My experience with people working under these kinds of arrangements is that they absolutely do think of their PTO in monetary terms, and manage it with an expectation that most of it will be turned into money at some point, and that anyone past the first couple years on the job has quite a bit "banked", so that "fining" them some PTO isn't preventing them from taking time off, but is taking (future) money away, and the employee would understand it in those terms.
Do you have any evidence that it is uncommon to take your vacation days, or is this just a bunch of anecdotes about workaholics? Vacation days wouldn't be a thing if workers didn't care about using them.
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.
