There are several reasons, but I’ll just give you two.
(1) In order to run a tournament with such a large number of people, people can’t be playing constantly.
(2) It also is part of our risk management plan to make sure that people are not getting too inebriated as a direct result of the tournament. We decided that one beer per hour from playing a beer pong game is not excessive drinking. This may sound stupid, but it is important because (1) it allows us to run the event safely so nobody gets hurt, and (2) without such controls, the casino’s risk management team would not be likely to let us run the event (and equally, we would not be willing to run the event).