They also have to pay for the associates who serve the Coke, the AC in the building, new attractions, licensing fees for certain archaic children's characters, new pavers, flagpoles, and arches... and that's just what I can think of off the top of my head. You aren't JUST paying for the Coke. And, besides, if you don't like it, feel free to get a FREE cup of water which would cost you at other parks...
You bring your own drinks into the park?