The Drink Package is 100% free, there is no lie or deception in their marketing. They never said "free gratuities". Anyone who buys the drink package also pays the gratuities on top of the drinks package price.
Also the term "gratuities" does not mean optional by definition. There are lots of businesses that have required, or mandatory, gratuities. One example would be a restaurant auto applying an 18% gratuities for large parties (6+ etc). The oxford English dictionary as: "money that you give to somebody who has provided a service for you"