Remember that the items that are done on a per-player basis, the TD needs to account for maximum attendance. It would reflect horribly on the TD if food/players Paks/drinks ran out. But, then the financial risk the TD assumes is that if less than the maximum turns out, all of these items potentially become a loss for the tournament budget.
Conversely, the fixed cost items (insurance, rental/usage fees, sanctioning, etc) become less on a per player basis the more players show up.
This makes it hard to plan since our culture is allowing sign-ups at the event. It also makes it hard to calculate and post a financial overview at the event.