It's unfathomable, tbh.
They probably way undershot the operating cost for a real water park.
EDIT: TapuTapu is also a weight on the place. When the park is packed, TapuTapu makes it seem like people can't do anything in the park without a 2 hour wait, which upsets people. Upset people don't spend money on food, drinks, and merch. They leave and demand a refund.
Parks don't make their money on admission. They make it on the stuff they sell inside.