Devil’s advocate: This dissuades guests from renting a larger locker if they only need a small. There are other ways to do that, like having TMs out there guarding the large ones and sending folks to small, but nothing keeps people from using something better than charging for it.
Case in point, the new paid fast lane being added down the center of I-4.
Now personally I don’t agree this is the best way to handle it, but I bet that it might have something to do with the decision, especially if the big ones are going first.