I think the PP has it just right. The parks have a uptick for the Holidays and rely on discounts less.
The main reason they do the 3 for 5 is to get you in the parks longer for vacation trips.
For myself I always go 3 day ph because it takes me a day to drive there and back. But for free getting a five may mean I get and hour or two when I arrive and before i leave. This means i might be buying Dinner or Breakfast in the park. And it a few more hours to see merchandise.
But it starts getting harder for everyone with Kids in school to leave for a week when school is going again.