Because not only does my employer have unlimited PTO policy, it has a mandatory minimum PTO policy.
It also has a mandatory minimum duration PTO policy.
As an employee, I MUST take at least 20 working days off per year, and among that time off there must be AT LEAST 10 working days taken off in a row, measured Monday - Friday for two weeks.
And federal holidays don't count for those 20 working days (though they do count for the two week minimum).
If I want to take two days off to binge-watch Seinfeld, I mark Thursday and Friday as "off" in our company app and my manager swings by my office and says "How's Project-X going?" and I say "on schedule" and he taps "approve" on his phone and then we talk about how I'm just going to lay around in my boxers and watch Seinfeld for four days in a row.
Of course, he already knows that Project-X is on schedule because he's in Mattermost the same as I, he just happened to pass by on his way to the cafeteria and wanted to chat about his new OneWheel and how awesome it is.
If, in December, you have not met your quota of 20 working days off, they order you to not come in for the balance counted back from New Year's Eve, not counting Christmas Day, and that is non-negotiable. They even suspend your accounts for the last two weeks of the year if you haven't met your two week obligation.